|**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 3120172016(In millions)Economic Useful LifeCarrying AmountAccumulated AmortizationCarrying AmountAccumulated AmortizationFinite-lived intangible assets:Trade name8 years$7$5$6$3Distribution channel15 years114103Total finite-lived intangible assets189166Indefinite-lived intangible assets:Syndicate capacity4743Agency force1616Total indefinite-lived intangible assets6359Total other intangible assets$81$9$75$6
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|December 31                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|(In millions)                                                | Economic Useful Life                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Finite-lived intangible assets:                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|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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