| **Property Casualty Loss and Loss Expenses**                | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
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| **Premiums Written, Net, Property and Casualty [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| Property Casualty Loss And Loss Expenses                    | PROPERTY CASUALTY LOSS AND LOSS EXPENSES This table summarizes activity for our consolidated property casualty loss and loss expense reserves: (In millions) Three months ended March 31,  2013 2012Gross loss and loss expense reserves, beginning of period $4,169 $4,280Less reinsurance receivable 356 375Net loss and loss expense reserves, beginning of period 3,813 3,905Net incurred loss and loss expenses related to:    Current accident year 534 655Prior accident years (10) (116)Total incurred 524 539Net paid loss and loss expenses related to:    Current accident year 121 132Prior accident years 392 375Total paid 513 507Net loss and loss expense reserves, end of period 3,824 3,937Plus reinsurance receivable 349 352Gross loss and loss expense reserves, end of period $4,173 $4,289 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 $67 million at March 31, 2013, and $58 million at March 31, 2012, for certain life and health loss and loss expense reserves.For the three months ended March 31, 2013, we experienced $10 million of favorable development on prior accident years, including $12 million favorable development in commercial lines, $4 million adverse development in personal lines and $2 million favorable development in excess and surplus lines. There was $7 million from favorable development of catastrophe losses for the three months ended March 31, 2013, compared with $22 million of favorable development of catastrophe losses that occurred for the three months ended March 31, 2012. |

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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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