|**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 3120222021(In millions)Economic Useful LifeGross Carrying AmountAccumulated AmortizationGross Carrying AmountAccumulated AmortizationFinite-lived intangible assets:Trade name8 years$6$6$7$7Distribution channel15 years107117Total finite-lived intangible assets16131814Indefinite-lived intangible assets:Syndicate capacity4247Agency force1616Insurance licenses10—Total indefinite-lived intangible assets6863Total other intangible assets$84$13$81$14
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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                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Insurance licenses                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Total indefinite-lived intangible assets                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Total other intangible assets                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     

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