|**Reinsurance (Tables)**                                                                               | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                     
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|**Reinsurance Disclosures [Abstract]**                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                     
|Earned Consolidated Property Casualty Insurance Premiums On Assumed And Ceded Business                 | Our consolidated statements of income include earned consolidated property casualty insurance premiums on assumed and ceded business:(Dollars in millions)Years ended December 31,201420132012Direct earned premiums$4,209$3,903$3,520Assumed earned premiums12119Ceded earned premiums(176)(201)(185)Earned premiums$4,045$3,713$3,344                                                                             
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|(Dollars in millions)                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                     
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|Direct earned premiums                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                     
|Assumed earned premiums                                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                     
|Ceded earned premiums                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                     
|Earned premiums                                                                                        |                                                                                                                                                                                                                                                                                                                                                                                                                     
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|Incurred Consolidated Property Casualty Insurance Loss And Loss Expenses On Assumed And Ceded Business | Our consolidated statements of income include incurred consolidated property casualty insurance loss and loss expenses on assumed and ceded business:(Dollars in millions)Years ended December 31,201420132012Direct incurred loss and loss expenses$2,661$2,323$2,235Assumed incurred loss and loss expenses6116Ceded incurred loss and loss expenses(40)(33)(104)Incurred loss and loss expenses$2,627$2,301$2,137
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|(Dollars in millions)                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                     
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|Direct incurred loss and loss expenses                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                     
|Assumed incurred loss and loss expenses                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                     
|Ceded incurred loss and loss expenses                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                     
|Incurred loss and loss expenses                                                                        |                                                                                                                                                                                                                                                                                                                                                                                                                     
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|Earned Life Insurance Premiums On Ceded Business                                                       | Our consolidated statements of income include earned life insurance premiums on ceded business:(Dollars in millions)Years ended December 31,201420132012Direct earned premiums$259$248$235Ceded earned premiums(61)(59)(57)Earned premiums$198$189$178                                                                                                                                                              
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|(Dollars in millions)                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                     
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|Direct earned premiums                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                     
|Ceded earned premiums                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                     
|Earned premiums                                                                                        |                                                                                                                                                                                                                                                                                                                                                                                                                     
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|Life Insurance Contract Holders' Benefits Incurred On Ceded Business                                   | Our consolidated statements of income include life insurance contract holders’ benefits incurred on ceded business:(Dollars in millions)Years ended December 31,201420132012Direct contract holders' benefits incurred$299$266$232Ceded contract holders' benefits incurred(70)(62)(47)Contract holders' benefits incurred$229$204$185                                                                              
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|(Dollars in millions)                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                     
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|Direct contract holders' benefits incurred                                                             |                                                                                                                                                                                                                                                                                                                                                                                                                     
|Ceded contract holders' benefits incurred                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                     
|Contract holders' benefits incurred                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                     
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