|**Reinsurance (Tables)**                                                                               | 6 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 June 30,Six months ended June 30,2014201320142013Direct earned premiums$1,048$958$2,067$1,893Assumed earned premiums2355Ceded earned premiums(44)(51)(87)(99)Net earned premiums$1,006$910$1,985$1,799                                                                            
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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 June 30,Six months ended June 30,2014201320142013Direct incurred loss and loss expenses$716$593$1,393$1,128Assumed incurred loss and loss expenses2547Ceded incurred loss and loss expenses(11)(15)(14)(28)Net incurred loss and loss expenses$707$583$1,383$1,107
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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 June 30,Six months ended June 30,2014201320142013Direct earned premiums$68$58$130$114Ceded earned premiums(15)(14)(29)(28)Net earned premiums$53$44$101$86                                                                                                                                                              
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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 contract holders' benefits incurred on ceded business:(In millions)Three months ended June 30,Six months ended June 30,2014201320142013Direct contract holders' benefits incurred$68$62$148$126Ceded contract holders' benefits incurred(12)(14)(36)(34)Net contract holders' benefits incurred$56$48$112$92                                                                              
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|(In millions)                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
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|Direct contract holders' benefits incurred                                                             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Ceded contract holders' benefits incurred                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Net contract holders' benefits incurred                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
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