| **Property Casualty Loss and Loss Expenses** | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
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| **Premiums Written, Net [Abstract]**         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| Property Casualty Loss And Loss Expenses     | PROPERTY CASUALTY LOSS AND LOSS EXPENSESThis table summarizes activity for our consolidated property casualty loss and loss expense reserves:(In millions) Three months ended March 31,  2014 2013Gross loss and loss expense reserves, beginning of period $4,241 $4,169Less reinsurance receivable 299 356Net loss and loss expense reserves, beginning of period 3,942 3,813Net incurred loss and loss expenses related to:    Current accident year 705 534Prior accident years (29) (10)Total incurred 676 524Net paid loss and loss expenses related to:    Current accident year 197 121Prior accident years 387 392Total paid 584 513Net loss and loss expense reserves, end of period 4,034 3,824Plus reinsurance receivable 289 349Gross loss and loss expense reserves, end of period $4,323 $4,173      We use actuarial methods, models and judgment to estimate, as of a financial statement date, the property casualty loss and loss expense reserves required to pay for and settle all outstanding insured claims, including incurred but not reported (IBNR) claims, as of that date. The actuarial estimate is subject to review and adjustment by an inter-departmental committee that includes actuarial management that is familiar with relevant company and industry business, claims and underwriting trends, as well as general economic and legal trends that could affect future loss and loss expense payments. The amount we will actually have to pay for claims can be highly uncertain. This uncertainty, together with the size of our reserves, makes the loss and loss expense reserves our most significant estimate. The reserve for loss and loss expenses in the condensed consolidated balance sheets also included $52 million at March 31, 2014, and $67 million at March 31, 2013, for certain life and health loss and loss expense reserves.For the three months ended March 31, 2014, we experienced $29 million of favorable development on prior accident years, including $3 million of favorable development in commercial lines, $17 million of favorable development in personal lines and $9 million favorable development in excess and surplus lines. This included$9 million from favorable development of catastrophe losses for the three months ended March 31, 2014, compared with $7 million of favorable development of catastrophe losses for the three months ended March 31, 2013. |

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| - Definition
The disclosure of the amount needed to reflect the estimated ultimate cost of settling claims relating to casualty insurance insured events that have occurred on or before a particular date (ordinarily, the balance sheet date) and the amount needed to provide for the estimated ultimate cost required to investigate and settle claims relating to insured events that have occurred on or before a particular date (ordinarily, the balance sheet date), whether or not reported to the insurer at that date. This disclosure is less life and health loss expense reserves.
+ References
No definition available.
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