|**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 31,201520142013Direct earned premiums$4,396$4,209$3,903Assumed earned premiums291211Ceded earned premiums(154)(176)(201)Earned premiums$4,271$4,045$3,713                                                                            
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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 31,201520142013Direct incurred loss and loss expenses$2,596$2,661$2,323Assumed incurred loss and loss expenses12611Ceded incurred loss and loss expenses(36)(40)(33)Incurred loss and loss expenses$2,572$2,627$2,301
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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 31,201520142013Direct earned premiums$271$259$248Ceded earned premiums(62)(61)(59)Earned premiums$209$198$189                                                                                                                                                              
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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 31,201520142013Direct contract holders' benefits incurred$292$299$266Ceded contract holders' benefits incurred(56)(70)(62)Contract holders' benefits incurred$236$229$204                                                                              
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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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