|**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:(In millions)Three months ended September 30,Nine months ended September 30,2013201220132012Direct earned premiums$1,002$898$2,895$2,605Assumed earned premiums3187Ceded earned premiums(51)(48)(150)(137)Net earned premiums$954$851$2,753$2,475                                                                             
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|(In millions)                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
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|Direct earned premiums                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Assumed earned premiums                                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Ceded earned premiums                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net earned premiums                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|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:(In millions)Three months ended September 30,Nine months ended September 30,2013201220132012Direct incurred loss and loss expenses$597$562$1,725$1,745Assumed incurred loss and loss expenses1(3)83Ceded incurred loss and loss expenses(5)(34)(33)(44)Net incurred loss and loss expenses$593$525$1,700$1,704
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|(In millions)                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
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|Direct incurred loss and loss expenses                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Assumed incurred loss and loss expenses                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Ceded incurred loss and loss expenses                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net incurred loss and loss expenses                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Earned Life Insurance Premiums On Ceded Business                                                       | Our condensed consolidated statements of income include earned life insurance premiums on ceded business:(In millions)Three months ended September 30,Nine months ended September 30,2013201220132012Direct earned premiums$52$52$166$170Assumed earned premiums————Ceded earned premiums(14)(14)(42)(40)Net earned premiums$38$38$124$130                                                                                                                                   
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|(In millions)                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
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|Direct earned premiums                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Assumed earned premiums                                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Ceded earned premiums                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net earned premiums                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Life Insurance Contract Holders' Benefits Incurred On Ceded Business                                   | Our condensed consolidated statements of income include life insurance policyholders’ benefits incurred on ceded business:(In millions)Three months ended September 30,Nine months ended September 30,2013201220132012Direct policyholders' benefits incurred$64$62$190$172Assumed policyholders' benefits incurred————Ceded policyholders' benefits incurred(15)(16)(49)(36)Net policyholders' benefits incurred$49$46$141$136                                              
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|(In millions)                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
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|Direct policyholders' benefits incurred                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Assumed policyholders' benefits incurred                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Ceded policyholders' benefits incurred                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net policyholders' benefits incurred                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                              

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