| **Reinsurance (Tables)**                                                                               | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
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| **Reinsurance Disclosures [Abstract]**                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| Earned Consolidated Property Casualty Insurance Premiums On Assumed And Ceded Business                 | Our condensed consolidated statements of income include earned consolidated property casualty insurance premiums on assumed and ceded business: (Dollars in millions) Three months ended September 30, Nine months ended September 30,  2016 2015 2016 2015Direct earned premiums $1,153 $1,110 $3,409 $3,279Assumed earned premiums 22 3 53 8Ceded earned premiums (42) (37) (119) (111)Earned premiums $1,133 $1,076 $3,343 $3,176                                                                        |
| Incurred Consolidated Property Casualty Insurance Loss And Loss Expenses On Assumed And Ceded Business | Our condensed consolidated statements of income include incurred consolidated property casualty insurance loss and loss expenses on assumed and ceded business:(Dollars in millions) Three months ended September 30, Nine months ended September 30,  2016 2015 2016 2015Direct incurred loss and loss expenses $691 $618 $2,131 $1,984Assumed incurred loss and loss expenses 9 2 30 2Ceded incurred loss and loss expenses (10) (7) (51) (30)Incurred loss and loss expenses $690 $613 $2,110 $1,956          |
| Earned Life Insurance Premiums On Ceded Business                                                       | Our condensed consolidated statements of income include earned life insurance premiums on ceded business: (Dollars in millions) Three months ended September 30, Nine months ended September 30,  2016 2015 2016 2015Direct earned premiums $74 $67 $220 $200Ceded earned premiums (16) (16) (45) (44)Earned premiums $58 $51 $175 $156                                                                                                                                                                                    |
| Life Insurance Contract Holders' Benefits Incurred On Ceded Business                                   | Our condensed consolidated statements of income include life insurance contract holders' benefits incurred on ceded business: (Dollars in millions) Three months ended September 30, Nine months ended September 30,  2016 2015 2016 2015Direct contract holders' benefits incurred $72 $70 $228 $214Ceded contract holders' benefits incurred (9) (13) (40) (39)Contract holders' benefits incurred $63 $57 $188 $175                                                                                                     |

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