|**Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions**                                                                                                                                                                                                                                                                                                                                                                                                            | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
|**Operating revenues**                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net earned premiums                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | $ 2,347                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       | $ 2,155                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Net investment income                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 575                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 432                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Non-insurance warranty revenue                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 407                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 392                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Other revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 7                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 6                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Total operating revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 3,336                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 2,985                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|**Claims, Benefits and Expenses**                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net incurred claims and benefits                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | 1,772                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 1,594                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Policyholders’ dividends                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 7                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 7                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Amortization of deferred acquisition costs                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 403                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 374                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Non-insurance warranty expense                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 384                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 367                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Other insurance related expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | 318                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 275                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Other expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 59                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 82                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Total claims, benefits and expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 2,943                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 2,699                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Core income (loss) before income tax                                                                                                                                                                                                                                                                                                                                                                                                                                                              | 393                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 286                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Income tax (expense) benefit on core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                | (85)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | (56)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | 308                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 230                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Net investment gains (losses)                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | (32)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | (59)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Income tax (expense) benefit on net investment gains (losses)                                                                                                                                                                                                                                                                                                                                                                                                                                     | 7                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 19                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Net investment gains (losses), after tax                                                                                                                                                                                                                                                                                                                                                                                                                                                          | (25)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | (40)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Net income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 283                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 190                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Operating Segments | Specialty                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|**Operating revenues**                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net earned premiums                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 812                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 794                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Net investment income                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 142                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 100                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Non-insurance warranty revenue                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 407                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 392                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Other revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Total operating revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 1,361                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 1,286                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|**Claims, Benefits and Expenses**                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net incurred claims and benefits                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | 474                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 456                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Policyholders’ dividends                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 2                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 2                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Amortization of deferred acquisition costs                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 168                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 162                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Non-insurance warranty expense                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 384                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 367                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Other insurance related expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | 94                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 81                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Other expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 12                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 12                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Total claims, benefits and expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 1,134                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 1,080                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Core income (loss) before income tax                                                                                                                                                                                                                                                                                                                                                                                                                                                              | 227                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 206                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Income tax (expense) benefit on core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                | (50)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | (45)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | 177                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 161                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Operating Segments | Commercial                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|**Operating revenues**                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net earned premiums                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 1,120                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 974                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Net investment income                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 165                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 113                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Non-insurance warranty revenue                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Other revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 6                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 4                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Total operating revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 1,291                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 1,091                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|**Claims, Benefits and Expenses**                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net incurred claims and benefits                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | 740                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 610                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Policyholders’ dividends                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 5                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 5                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Amortization of deferred acquisition costs                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 175                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 156                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Non-insurance warranty expense                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Other insurance related expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | 158                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 134                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Other expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 10                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 11                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Total claims, benefits and expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 1,088                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 916                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Core income (loss) before income tax                                                                                                                                                                                                                                                                                                                                                                                                                                                              | 203                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 175                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Income tax (expense) benefit on core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                | (44)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | (37)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | 159                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 138                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Operating Segments | International                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|**Operating revenues**                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net earned premiums                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 302                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 269                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Net investment income                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 25                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 14                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Non-insurance warranty revenue                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Other revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 1                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 1                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Total operating revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 328                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 284                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|**Claims, Benefits and Expenses**                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net incurred claims and benefits                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | 185                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 160                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Policyholders’ dividends                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Amortization of deferred acquisition costs                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 60                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 56                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Non-insurance warranty expense                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Other insurance related expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | 35                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 30                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Other expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | (5)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 13                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Total claims, benefits and expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 275                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 259                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Core income (loss) before income tax                                                                                                                                                                                                                                                                                                                                                                                                                                                              | 53                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 25                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Income tax (expense) benefit on core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                | (15)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | (7)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | 38                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 18                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Operating Segments | Life & Group                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|**Operating revenues**                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net earned premiums                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 113                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 118                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Net investment income                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 229                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 201                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Non-insurance warranty revenue                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Other revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 1                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Total operating revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 342                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 320                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|**Claims, Benefits and Expenses**                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net incurred claims and benefits                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | 344                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 311                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Policyholders’ dividends                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Amortization of deferred acquisition costs                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Non-insurance warranty expense                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Other insurance related expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | 31                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 29                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Other expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 2                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Total claims, benefits and expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 375                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 342                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Core income (loss) before income tax                                                                                                                                                                                                                                                                                                                                                                                                                                                              | (33)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | (22)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Income tax (expense) benefit on core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                | 13                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 13                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | (20)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | (9)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Operating Segments | Corporate & Other                                                                                                                                                                                                                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|**Operating revenues**                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net earned premiums                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Net investment income                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 14                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 4                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Non-insurance warranty revenue                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Other revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 2                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 1                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Total operating revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 16                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 5                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|**Claims, Benefits and Expenses**                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net incurred claims and benefits                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | 29                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 57                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Policyholders’ dividends                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Amortization of deferred acquisition costs                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Non-insurance warranty expense                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Other insurance related expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 1                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Other expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 44                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 45                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Total claims, benefits and expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 73                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 103                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Core income (loss) before income tax                                                                                                                                                                                                                                                                                                                                                                                                                                                              | (57)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | (98)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Income tax (expense) benefit on core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                | 11                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 20                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | (46)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | (78)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Eliminations                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|**Operating revenues**                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net earned premiums                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Net investment income                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Non-insurance warranty revenue                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Other revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | (2)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | (1)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Total operating revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | (2)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | (1)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|**Claims, Benefits and Expenses**                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net incurred claims and benefits                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Policyholders’ dividends                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Amortization of deferred acquisition costs                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Non-insurance warranty expense                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Other insurance related expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Other expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | (2)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | (1)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Total claims, benefits and expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                               | (2)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | (1)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Core income (loss) before income tax                                                                                                                                                                                                                                                                                                                                                                                                                                                              | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Income tax (expense) benefit on core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | $ 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | $ 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|[1]
As of January 1, 2023, the Company adopted  ASU 2018-12, Financial Services-Insurance (Topic 944): Targeted Improvements to the Accounting for Long-Duration Contracts(ASU 2018-12) using the modified retrospective method applied as of the transition date of January 1, 2021.  Prior period amounts in the financial statements have been adjusted to reflect application of the new guidance.  See Note A to the Condensed Consolidated Financial Statements for additional information. | [1]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | As of January 1, 2023, the Company adopted  ASU 2018-12, Financial Services-Insurance (Topic 944): Targeted Improvements to the Accounting for Long-Duration Contracts(ASU 2018-12) using the modified retrospective method applied as of the transition date of January 1, 2021.  Prior period amounts in the financial statements have been adjusted to reflect application of the new guidance.  See Note A to the Condensed Consolidated Financial Statements for additional information.
|[1]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | As of January 1, 2023, the Company adopted  ASU 2018-12, Financial Services-Insurance (Topic 944): Targeted Improvements to the Accounting for Long-Duration Contracts(ASU 2018-12) using the modified retrospective method applied as of the transition date of January 1, 2021.  Prior period amounts in the financial statements have been adjusted to reflect application of the new guidance.  See Note A to the Condensed Consolidated Financial Statements for additional information.

X- DefinitionCosts From Contract With Customers
+ ReferencesNo definition available.
+ Details**Name:**
cna_CostsFromContractWithCustomers**Namespace Prefix:**
cna_**Data Type:**
xbrli:monetaryItemType**Balance Type:**
debit**Period Type:**
duration X- DefinitionIncome Tax Expense (Benefit) on Net Realized Investment Gains Losses
+ ReferencesNo definition available.
+ Details**Name:**
cna_IncomeTaxExpenseBenefitOnNetRealizedInvestmentGainsLosses**Namespace Prefix:**
cna_**Data Type:**
xbrli:monetaryItemType**Balance Type:**
debit**Period Type:**
duration X- DefinitionIncome Tax Expense (Benefit) on Operating Income (Loss)
+ ReferencesNo definition available.
+ Details**Name:**
cna_IncomeTaxExpenseBenefitOnOperatingIncomeLoss**Namespace Prefix:**
cna_**Data Type:**
xbrli:monetaryItemType**Balance Type:**
debit**Period Type:**
duration X- DefinitionThe income earned from investments in securities and property, equipment and other capital assets. It includes rent from property and equipment, dividends from shares in corporations, and interest from bonds, loans, mortgages, derivatives, commercial paper, bank accounts, certificates of deposits, treasuries, and other financial securities. It also includes realized gains and losses on trading securities.
+ ReferencesNo definition available.
+ Details**Name:**
cna_NetInvestmentIncomeAndGainsLossesOnTradingSecurities**Namespace Prefix:**
cna_**Data Type:**
xbrli:monetaryItemType**Balance Type:**
credit**Period Type:**
duration X- DefinitionNet Operating Income (Loss) Attributable to Parent
+ ReferencesNo definition available.
+ Details**Name:**
cna_NetOperatingIncomeLossFromContinuingOperationsAttributabletoParent**Namespace Prefix:**
cna_**Data Type:**
xbrli:monetaryItemType**Balance Type:**
credit**Period Type:**
duration X- DefinitionNet Realized Investment Gains (Losses)
+ ReferencesNo definition available.
+ Details**Name:**
cna_NetRealizedInvestmentGainsLosses**Namespace Prefix:**
cna_**Data Type:**
xbrli:monetaryItemType**Balance Type:**
credit**Period Type:**
duration X- DefinitionOperating Income (Loss) before Income Tax
+ ReferencesNo definition available.
+ Details**Name:**
cna_OperatingIncomeLossFromContinuingOperationsBeforeIncomeTax**Namespace Prefix:**
cna_**Data Type:**
xbrli:monetaryItemType**Balance Type:**
credit**Period Type:**
duration X- DefinitionOperating Revenues
+ ReferencesNo definition available.
+ Details**Name:**
cna_OperatingRevenues**Namespace Prefix:**
cna_**Data Type:**
xbrli:monetaryItemType**Balance Type:**
credit**Period Type:**
duration X- DefinitionOther Insurance Related Expenses
+ ReferencesNo definition available.
+ Details**Name:**
cna_OtherInsuranceRelatedExpenses**Namespace Prefix:**
cna_**Data Type:**
xbrli:monetaryItemType**Balance Type:**
debit**Period Type:**
duration X- DefinitionThe total amount of expense recognized during the period for future policy benefits, claims and claims adjustment costs, and for selling, general and administrative costs.
+ ReferencesReference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.5,6,7) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1
+ Details**Name:**
us-gaap_BenefitsLossesAndExpenses**Namespace Prefix:**
us-gaap_**Data Type:**
xbrli:monetaryItemType**Balance Type:**
debit**Period Type:**
duration X- ReferencesNo definition available.
+ Details**Name:**
us-gaap_BenefitsLossesAndExpensesAbstract**Namespace Prefix:**
us-gaap_**Data Type:**
xbrli:stringItemType**Balance Type:**
na**Period Type:**
duration X- DefinitionAmount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), investment in debt security measured at amortized cost (held-to-maturity) and investment in debt security measured at fair value with change in fair value recognized in net income (trading).
+ ReferencesReference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(7)(c)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(9)(a)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(3)(d)(1)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1
+ Details**Name:**
us-gaap_DebtSecuritiesRealizedGainLoss**Namespace Prefix:**
us-gaap_**Data Type:**
xbrli:monetaryItemType**Balance Type:**
credit**Period Type:**
duration X- DefinitionAmount of amortization expense (reversal of expense) for deferred policy acquisition costs.
+ ReferencesReference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 65 -Paragraph 2 -Subparagraph (g)(1) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480016/944-40-65-2Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Topic 944 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479432/944-30-50-2Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 2B -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479432/944-30-50-2BReference 4: http://www.xbrl.org/2003/role/exampleRef -Topic 944 -SubTopic 30 -Name Accounting Standards Codification -Section 55 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479401/944-30-55-2Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 2 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479868/944-20-45-2Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 230 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482740/230-10-45-28Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(7)(a)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479432/944-30-50-1
+ Details**Name:**
us-gaap_DeferredPolicyAcquisitionCostAmortizationExpense**Namespace Prefix:**
us-gaap_**Data Type:**
xbrli:monetaryItemType**Balance Type:**
debit**Period Type:**
duration X- DefinitionAmount after tax of income (loss) from continuing operations attributable to the parent.
+ ReferencesReference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 250 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org//1943274/2147483443/250-10-50-3Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 250 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 11 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483443/250-10-50-11Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 250 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 11 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483443/250-10-50-11Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 250 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4 -Publisher FASB -URI https://asc.fasb.org//1943274/2147483443/250-10-50-4Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 260 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482662/260-10-50-1Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 260 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 60B -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482689/260-10-45-60BReference 7: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 230 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482740/230-10-45-28Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481231/810-10-45-18Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.13) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2
+ Details**Name:**
us-gaap_IncomeLossFromContinuingOperations**Namespace Prefix:**
us-gaap_**Data Type:**
xbrli:monetaryItemType**Balance Type:**
credit**Period Type:**
duration X- DefinitionAmount of expense classified as other.
+ ReferencesReference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.4,6) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2
+ Details**Name:**
us-gaap_OtherExpenses**Namespace Prefix:**
us-gaap_**Data Type:**
xbrli:monetaryItemType**Balance Type:**
debit**Period Type:**
duration X- DefinitionAmount of revenue and income classified as other.
+ ReferencesReference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 320 -Name Accounting Standards Codification -Section S99 -Paragraph 6 -Subparagraph (SX 210.12-14(Column E)(2)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480032/946-320-S99-6Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 320 -Name Accounting Standards Codification -Section S99 -Paragraph 6 -Subparagraph (SX 210.12-14(Column E)(Footnote 4)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480032/946-320-S99-6Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 320 -Name Accounting Standards Codification -Section S99 -Paragraph 6 -Subparagraph (SX 210.12-14(Column E)(Footnote 6)(b)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480032/946-320-S99-6Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(4)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-07(1)(c)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1
+ Details**Name:**
us-gaap_OtherIncome**Namespace Prefix:**
us-gaap_**Data Type:**
xbrli:monetaryItemType**Balance Type:**
credit**Period Type:**
duration X- DefinitionAmount, after effects of policies assumed or ceded, of expense related to the provision for policy benefits and costs incurred.
+ ReferencesReference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(5)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1
+ Details**Name:**
us-gaap_PolicyholderBenefitsAndClaimsIncurredNet**Namespace Prefix:**
us-gaap_**Data Type:**
xbrli:monetaryItemType**Balance Type:**
debit**Period Type:**
duration X- DefinitionAmount of expense for dividends to policyholders.
+ ReferencesReference 1: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(6)) -SubTopic 220 -Topic 944 -Publisher FASB -URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c) -SubTopic 50 -Topic 944 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479756/944-50-50-1
+ Details**Name:**
us-gaap_PolicyholderDividends**Namespace Prefix:**
us-gaap_**Data Type:**
xbrli:monetaryItemType**Balance Type:**
debit**Period Type:**
duration X- DefinitionAmount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned.
+ ReferencesReference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 235 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.12-17(Column E)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480149/944-235-S99-2Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 605 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c)(3) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479655/944-605-50-1Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04(13)(c)) -SubTopic 220 -Topic 942 -Publisher FASB -URI https://asc.fasb.org//1943274/2147483589/942-220-S99-1Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(1)) -SubTopic 220 -Topic 944 -Publisher FASB -URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1
+ Details**Name:**
us-gaap_PremiumsEarnedNet**Namespace Prefix:**
us-gaap_**Data Type:**
xbrli:monetaryItemType**Balance Type:**
credit**Period Type:**
duration X- DefinitionAmount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.
+ ReferencesReference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 924 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 11.L) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479941/924-10-S99-1Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 606 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479806/606-10-50-5Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 30 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482810/280-10-50-30Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 42 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482810/280-10-50-42Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 22 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482810/280-10-50-22Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 32 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482810/280-10-50-32Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 40 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482810/280-10-50-40Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 22 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482810/280-10-50-22Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 32 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482810/280-10-50-32Reference 10: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 41 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482810/280-10-50-41Reference 11: http://www.xbrl.org/2003/role/disclosureRef -Topic 606 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479806/606-10-50-4
+ Details**Name:**
us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax**Namespace Prefix:**
us-gaap_**Data Type:**
xbrli:monetaryItemType**Balance Type:**
credit**Period Type:**
duration X- ReferencesNo definition available.
+ Details**Name:**
us-gaap_RevenuesAbstract**Namespace Prefix:**
us-gaap_**Data Type:**
xbrli:stringItemType**Balance Type:**
na**Period Type:**
duration X- Details**Name:**
srt_ConsolidationItemsAxis=us-gaap_OperatingSegmentsMember**Namespace Prefix:****Data Type:**
na**Balance Type:****Period Type:** X- Details**Name:**
us-gaap_StatementBusinessSegmentsAxis=cna_SpecialtySegmentMember**Namespace Prefix:****Data Type:**
na**Balance Type:****Period Type:** X- Details**Name:**
us-gaap_StatementBusinessSegmentsAxis=cna_CommercialSegmentMember**Namespace Prefix:****Data Type:**
na**Balance Type:****Period Type:** X- Details**Name:**
us-gaap_StatementBusinessSegmentsAxis=cna_InternationalSegmentMember**Namespace Prefix:****Data Type:**
na**Balance Type:****Period Type:** X- Details**Name:**
us-gaap_StatementBusinessSegmentsAxis=cna_LifeAndGroupNonCoreSegmentMember**Namespace Prefix:****Data Type:**
na**Balance Type:****Period Type:** X- Details**Name:**
us-gaap_StatementBusinessSegmentsAxis=us-gaap_CorporateAndOtherMember**Namespace Prefix:****Data Type:**
na**Balance Type:****Period Type:** X- Details**Name:**
srt_ConsolidationItemsAxis=us-gaap_IntersegmentEliminationMember**Namespace Prefix:****Data Type:**
na**Balance Type:****Period Type:**