|**Reinsurance (Tables)**                                                                               | 3 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 March 31,20142013Direct earned premiums$1,019$935Assumed earned premiums32Ceded earned premiums(43)(48)Net earned premiums$979$889                                                                             
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|(In millions)                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                               
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|Direct earned premiums                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                               
|Assumed earned premiums                                                                                |                                                                                                                                                                                                                                                                                                                                                                                               
|Ceded earned premiums                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                               
|Net earned premiums                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                               
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|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 March 31,20142013Direct incurred loss and loss expenses$677$535Assumed incurred loss and loss expenses22Ceded incurred loss and loss expenses(3)(13)Net incurred loss and loss expenses$676$524
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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                                                                    |                                                                                                                                                                                                                                                                                                                                                                                               
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|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 March 31,20142013Direct earned premiums$62$56Ceded earned premiums(14)(14)Net earned premiums$48$42                                                                                                                                                  
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|(In millions)                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                               
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|Direct earned premiums                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                               
|Ceded earned premiums                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                               
|Net earned premiums                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                               
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|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 March 31,20142013Direct policyholders' benefits incurred$80$64Ceded policyholders' benefits incurred(24)(20)Net policyholders' benefits incurred$56$44                                                                              
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|(In millions)                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                               
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|Direct policyholders' benefits incurred                                                                |                                                                                                                                                                                                                                                                                                                                                                                               
|Ceded policyholders' benefits incurred                                                                 |                                                                                                                                                                                                                                                                                                                                                                                               
|Net policyholders' benefits incurred                                                                   |                                                                                                                                                                                                                                                                                                                                                                                               
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