|**Life Policy And Investment Contract Reserves (Tables)**                                                                 | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                     
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|**Liability for Future Policy Benefits [Abstract]**                                                                       |                                                                                                                                                                                                                                                                                                                                                                                                     
|Reserve In Addition To The Account Balance, Based on Expected No-Lapse Guarantee Benefits And Expected Policy Assessments | This table summarizes our life policy and investment contract reserves:(Dollars in millions)At December 31,20172016Life policy reserves:Ordinary/traditional life$1,080$1,011Other4745Subtotal1,1271,056Investment contract reserves:Deferred annuities835861Universal life601578Structured settlements160170Other66Subtotal1,6021,615Total life policy and investment contract reserves$2,729$2,671
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|(Dollars in millions)                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                     
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|Life policy reserves:                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                     
|Ordinary/traditional life                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                     
|Other                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                     
|Subtotal                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                     
|Investment contract reserves:                                                                                             |                                                                                                                                                                                                                                                                                                                                                                                                     
|Deferred annuities                                                                                                        |                                                                                                                                                                                                                                                                                                                                                                                                     
|Universal life                                                                                                            |                                                                                                                                                                                                                                                                                                                                                                                                     
|Structured settlements                                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                     
|Other                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                     
|Subtotal                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                     
|Total life policy and investment contract reserves                                                                        |                                                                                                                                                                                                                                                                                                                                                                                                     
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