|**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 3120192018(In millions)Economic Useful LifeGross Carrying AmountAccumulated AmortizationGross Carrying AmountAccumulated AmortizationFinite-lived intangible assets:Trade name8 years$7$6$6$5Distribution channel15 years115104Total finite-lived intangible assets1811169Indefinite-lived intangible assets:Syndicate capacity4645Agency force1616Total indefinite-lived intangible assets6261Total other intangible assets$80$11$77$9
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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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