|**Life Policy and Investment Contract Reserves (Tables)**      | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                              
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|**Liability for Future Policy Benefits [Abstract]**            |                                                                                                                                                                                                                                                                                                                                                                                                             
|Reserve For Losses Loss Adjustment Expenses Table [Text Block] | This table summarizes our life policy and investment contract reserves:(Dollars in millions)March 31, 2018December 31, 2017Life policy reserves:Ordinary/traditional life$1,098$1,080Other4747Subtotal1,1451,127Investment contract reserves:Deferred annuities821835Universal life607601Structured settlements161160Other66Subtotal1,5951,602Total life policy and investment contract reserves$2,740$2,729
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|(Dollars in millions)                                          |                                                                                                                                                                                                                                                                                                                                                                                                             
|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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duration X- DefinitionThe entire disclosure for the present values of future benefits to be paid to or on behalf of policyholders and related expenses less the present value of future net premiums using assumptions such as estimates of expected investment yields, mortality, morbidity, terminations and expenses, applicable at the time the insurance contracts are made and unpaid claim costs relating to insurance contracts including estimates of costs relating to incurred but not reported claims based on the estimated ultimate cost of settling the claims (including effects of inflation and other societal and economic factors), using past experience adjusted for current trends and any other factors that would modify past experience by element such as business segment, country and interest rate range.
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