| **Property Casualty Loss and Loss Expenses (Tables)**         | 6 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 June 30, Six months ended June 30,  2014 2013 2014 2013Gross loss and loss expense reserves, beginning  of period $4,323 $4,173 $4,241 $4,169Less reinsurance receivable 289 349 299 356Net loss and loss expense reserves, beginning of  period 4,034 3,824 3,942 3,813Net incurred loss and loss expenses related to:        Current accident year 773 675 1,478 1,209Prior accident years (66) (92) (95) (102)Total incurred 707 583 1,383 1,107Net paid loss and loss expenses related to:        Current accident year 309 249 506 370Prior accident years 306 272 693 664Total paid 615 521 1,199 1,034Net loss and loss expense reserves, end of period 4,126 3,886 4,126 3,886Plus reinsurance receivable 282 333 282 333Gross loss and loss expense reserves, end of  period $4,408 $4,219 $4,408 $4,219          |

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Consolidated Property Casualty Loss And Loss Expense Reserves
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