|**Property Casualty Loss and Loss Expenses (Tables)**         | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
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|**Premiums Written, Net [Abstract]**                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Consolidated Property Casualty Loss And Loss Expense Reserves | This table summarizes activity for our consolidated property casualty loss and loss expense reserves:(In millions)Three months ended March 31,20142013Gross loss and loss expense reserves, beginning of period$4,241$4,169Less reinsurance receivable299356Net loss and loss expense reserves, beginning of period3,9423,813Net incurred loss and loss expenses related to:Current accident year705534Prior accident years(29)(10)Total incurred676524Net paid loss and loss expenses related to:Current accident year197121Prior accident years387392Total paid584513Net loss and loss expense reserves, end of period4,0343,824Plus reinsurance receivable289349Gross loss and loss expense reserves, end of period$4,323$4,173
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|(In millions)                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
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|Gross loss and loss expense reserves, beginning of period     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Less reinsurance receivable                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Net loss and loss expense reserves, beginning of period       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Net incurred loss and loss expenses related to:               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Current accident year                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Prior accident years                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Total incurred                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Net paid loss and loss expenses related to:                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Current accident year                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Prior accident years                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Total paid                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Net loss and loss expense reserves, end of period             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Plus reinsurance receivable                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Gross loss and loss expense reserves, end of period           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
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