|**Accumulated Other Comprehensive Income (Loss) by Component (Tables)**                                                           | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
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|**Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]**                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Accumulated Other Comprehensive Income (Loss) by Component                                                                        | The tables below display the changes in Accumulated other comprehensive income (loss) by component. (In millions)Net unrealized gains (losses) on investments with OTTI lossesNet unrealized gains (losses) on other investmentsPension and postretirement benefitsCumulative foreign currency translation adjustmentTotalBalance as of January 1, 2019$16$61$(775)$(180)$(878)Other comprehensive income (loss) before reclassifications4521(1)17541Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit of $-, $1, $2, $- and $3—(5)(8)—(13)Other comprehensive income (loss) net of tax (expense) benefit of $(1), $(141), $(2), $- and $(144)4526717554Balance as of March 31, 2019$20$587$(768)$(163)$(324)(In millions)Net unrealized gains (losses) on investments with OTTI lossesNet unrealized gains (losses) on other investmentsPension and postretirement benefitsCumulative foreign currency translation adjustmentTotalBalance as of January 1, 2018$30$859$(775)$(98)$16Other comprehensive income (loss) before reclassifications(10)(414)—12(412)Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit of $-, $(4), $3, $- and $(1)(1)15(10)—4Other comprehensive income (loss) net of tax (expense) benefit of $2, $109, $(3), $- and $108(9)(429)1012(416)Balance as of March 31, 2018$21$430$(765)$(86)$(400)
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|(In millions)                                                                                                                     | Net unrealized gains (losses) on investments with OTTI losses                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Balance as of January 1, 2019                                                                                                     | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Other comprehensive income (loss) before reclassifications                                                                        | 4                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit of $-, $1, $2, $- and $3     | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Other comprehensive income (loss) net of tax (expense) benefit of $(1), $(141), $(2), $- and $(144)                               | 4                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Balance as of March 31, 2019                                                                                                      | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
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|(In millions)                                                                                                                     | Net unrealized gains (losses) on investments with OTTI losses                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Balance as of January 1, 2018                                                                                                     | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Other comprehensive income (loss) before reclassifications                                                                        | (10                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit of $-, $(4), $3, $- and $(1) | (1                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Other comprehensive income (loss) net of tax (expense) benefit of $2, $109, $(3), $- and $108                                     | (9                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Balance as of March 31, 2018                                                                                                      | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Reclassification out of Accumulated Other Comprehensive Income                                                                    | Amounts reclassified from Accumulated other comprehensive income (loss) shown above are reported in Net income (loss) as follows:Component of AOCIConsolidated Statements of Operations Line Item Affected by ReclassificationsNet unrealized gains (losses) on investments with OTTI lossesNet investment gains (losses)Net unrealized gains (losses) on other investmentsNet investment gains (losses)Pension and postretirement benefitsOther operating expenses and Insurance claims and policyholders' benefits                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
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|Component of AOCI                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Net unrealized gains (losses) on investments with OTTI losses                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Net unrealized gains (losses) on other investments                                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Pension and postretirement benefits                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  

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