|**Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions**                                                                                                                                                                                                                                                                                                                                                                                                           | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
|**Operating revenues**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Net earned premiums                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | $ 2,406                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | $ 2,221                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Net investment income                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 553                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 422                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Non-insurance warranty revenue                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 407                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 399                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Other revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 8                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 11                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Total operating revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 3,374                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 3,053                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|**Claims, Benefits and Expenses**                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Net incurred claims and benefits                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 1,818                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 1,873                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Policyholders’ dividends                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 8                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 7                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Amortization of deferred acquisition costs                                                                                                                                                                                                                                                                                                                                                                                                                                                       | 426                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 383                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Non-insurance warranty expense                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 386                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 371                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Other insurance related expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 294                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 297                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Other expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 78                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 77                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Total claims, benefits and expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                              | 3,010                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 3,008                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Core income (loss) before income tax                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 364                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 45                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Income tax (expense) benefit on core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                               | (75)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | (2)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 289                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 43                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Net investment gains (losses)                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | (38)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | (96)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Income tax (expense) benefit on net investment gains (losses)                                                                                                                                                                                                                                                                                                                                                                                                                                    | 7                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 11                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Net investment gains (losses), after tax                                                                                                                                                                                                                                                                                                                                                                                                                                                         | (31)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | (85)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Net income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | 258                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | (42)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Operating Segments | Specialty                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|**Operating revenues**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Net earned premiums                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | 829                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 810                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Net investment income                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 136                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 102                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Non-insurance warranty revenue                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 407                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 399                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Other revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | (1)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Total operating revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 1,372                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 1,310                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|**Claims, Benefits and Expenses**                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Net incurred claims and benefits                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 480                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 459                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Policyholders’ dividends                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 2                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 2                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Amortization of deferred acquisition costs                                                                                                                                                                                                                                                                                                                                                                                                                                                       | 175                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 169                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Non-insurance warranty expense                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 386                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 371                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Other insurance related expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 89                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 88                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Other expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 13                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 15                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Total claims, benefits and expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                              | 1,145                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 1,104                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Core income (loss) before income tax                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 227                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 206                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Income tax (expense) benefit on core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                               | (49)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | (45)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 178                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 161                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Operating Segments | Commercial                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|**Operating revenues**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Net earned premiums                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | 1,170                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 1,023                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Net investment income                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 156                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 112                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Non-insurance warranty revenue                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Other revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 9                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 13                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Total operating revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 1,335                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 1,148                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|**Claims, Benefits and Expenses**                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Net incurred claims and benefits                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 807                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 733                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Policyholders’ dividends                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 6                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 5                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Amortization of deferred acquisition costs                                                                                                                                                                                                                                                                                                                                                                                                                                                       | 188                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 163                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Non-insurance warranty expense                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Other insurance related expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 156                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 145                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Other expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 11                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 3                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Total claims, benefits and expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                              | 1,168                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 1,049                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Core income (loss) before income tax                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 167                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 99                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Income tax (expense) benefit on core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                               | (34)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | (19)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 133                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 80                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Operating Segments | International                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|**Operating revenues**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Net earned premiums                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | 296                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 270                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Net investment income                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 26                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 16                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Non-insurance warranty revenue                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Other revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | (1)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Total operating revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 321                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 286                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|**Claims, Benefits and Expenses**                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Net incurred claims and benefits                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 178                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 169                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Policyholders’ dividends                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Amortization of deferred acquisition costs                                                                                                                                                                                                                                                                                                                                                                                                                                                       | 63                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 51                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Non-insurance warranty expense                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Other insurance related expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 20                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 35                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Other expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 6                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 11                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Total claims, benefits and expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                              | 267                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 266                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Core income (loss) before income tax                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 54                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 20                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Income tax (expense) benefit on core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                               | (14)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | (1)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 40                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 19                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Operating Segments | Life & Group                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|**Operating revenues**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Net earned premiums                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | 112                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 118                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Net investment income                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 216                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 187                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Non-insurance warranty revenue                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Other revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Total operating revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 328                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 305                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|**Claims, Benefits and Expenses**                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Net incurred claims and benefits                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 343                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 525                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Policyholders’ dividends                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Amortization of deferred acquisition costs                                                                                                                                                                                                                                                                                                                                                                                                                                                       | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Non-insurance warranty expense                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Other insurance related expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 29                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 29                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Other expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | (1)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 2                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Total claims, benefits and expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                              | 371                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 556                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Core income (loss) before income tax                                                                                                                                                                                                                                                                                                                                                                                                                                                             | (43)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | (251)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Income tax (expense) benefit on core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                               | 14                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 59                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | (29)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | (192)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Operating Segments | Corporate & Other                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|**Operating revenues**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Net earned premiums                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Net investment income                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 19                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 5                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Non-insurance warranty revenue                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Other revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 2                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 1                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Total operating revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 21                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 6                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Claims, Benefits and Expenses**                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Net incurred claims and benefits                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 10                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | (13)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Policyholders’ dividends                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Amortization of deferred acquisition costs                                                                                                                                                                                                                                                                                                                                                                                                                                                       | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Non-insurance warranty expense                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Other insurance related expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 1                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 1                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Other expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 51                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 47                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Total claims, benefits and expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                              | 62                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 35                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Core income (loss) before income tax                                                                                                                                                                                                                                                                                                                                                                                                                                                             | (41)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | (29)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Income tax (expense) benefit on core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                               | 8                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 4                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Core income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | (33)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | (25)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Eliminations                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|**Operating revenues**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Net earned premiums                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | (1)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Net investment income                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Non-insurance warranty revenue                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Other revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | (2)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | (2)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Total operating revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | (3)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | (2)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|**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                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | (1)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | (1)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Other expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | (2)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | (1)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Total claims, benefits and expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                              | (3)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | (2)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|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:**