|**IT Transformation Costs by Segment (Tables)**   | 12 Months Ended                                                                                                                                                                           
|------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
|**IT transformation costs by segment [Abstract]** |                                                                                                                                                                                           
|IT transformation costs by segment                | IT Transformation Costs by SegmentYear ended December 31(In millions)2010CNA Specialty$8CNA Commercial15Life & Group Non-Core10Corporate & Other Non-Core3Total IT Transformation Costs$36
|                                                 
|                                                  |                                                                                                                                                                                           
|Year ended December 31                            |                                                                                                                                                                                           
|(In millions)                                     | 2010                                                                                                                                                                                      
|CNA Specialty                                     | $                                                                                                                                                                                         
|CNA Commercial                                    | 15                                                                                                                                                                                        
|Life & Group Non-Core                             | 10                                                                                                                                                                                        
|Corporate & Other Non-Core                        | 3                                                                                                                                                                                         
|Total IT Transformation Costs                     | $                                                                                                                                                                                         

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