|**Other Intangible Assets (Tables)**                         | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
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|**Intangible Assets, Gross (Excluding Goodwill) [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Schedule of Other Intangible Assets                          | Other intangible assets are presented in the following table.December 3120152014(In millions)Economic Useful LifeGross Carrying AmountAccumulated AmortizationGross Carrying AmountAccumulated AmortizationFinite-lived intangible assets:Value of business acquired1 - 4 years$57$57$60$61Trade name8 years7383Distribution channel15 years123122Total finite-lived intangible assets76638066Indefinite-lived intangible assets:Syndicate capacity5255Agency force1616Total indefinite-lived intangible assets6871Total other intangible assets$144$63$151$66
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|December 31                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|(In millions)                                                | Economic Useful Life                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Finite-lived intangible assets:                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Value of business acquired                                   | 1 - 4 years                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Trade name                                                   | 8 years                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Distribution channel                                         | 15 years                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Total finite-lived intangible assets                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Indefinite-lived intangible assets:                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Syndicate capacity                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Agency force                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Total indefinite-lived intangible assets                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Total other intangible assets                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               

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