| **IT Transformation**            | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
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| **IT Transformation [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| IT Transformation                | Note P. IT TransformationIn 2010, the Company commenced a program to significantly transform its IT organization and delivery model. A key initiative was moving to a managed services model which involved outsourcing the Company's infrastructure and application development functions to selected vendors that possess proven skills and scale.  Total costs of the program were $37 million, of which $36 million were incurred in 2010.  The costs by reportable segment for the year ended December 31, 2010 were as follows.IT Transformation Costs by SegmentYear ended December 31 (In millions)2010CNA Specialty$8CNA Commercial15Life & Group Non-Core10Corporate & Other Non-Core3Total IT Transformation Costs$36 |

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| - Definition
IT Transformation Disclosure
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No definition available.
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