| **Property Casualty Loss and Loss Expenses** | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
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| **Premiums Written, Net [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 June 30, Six months ended June 30,  2013 2012 2013 2012Gross loss and loss expense reserves, beginning of period $4,173 $4,289 $4,169 $4,280Less reinsurance receivable 349 352 356 375Net loss and loss expense reserves, beginning of period 3,824 3,937 3,813 3,905Net incurred loss and loss expenses related to:        Current accident year 675 725 1,209 1,380Prior accident years (92) (85) (102) (201)Total incurred 583 640 1,107 1,179Net paid loss and loss expenses related to:        Current accident year 249 282 370 414Prior accident years 272 290 664 665Total paid 521 572 1,034 1,079Net loss and loss expense reserves, end of period 3,886 4,005 3,886 4,005Plus reinsurance receivable 333 332 333 332Gross loss and loss expense reserves, end of period $4,219 $4,337 $4,219 $4,337 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 $65 million at June 30, 2013, and $59 million at June 30, 2012, for certain life and health loss and loss expense reserves.For the three months ended June 30, 2013, we experienced $92 million of favorable development on prior accident years, including $66 million of favorable development in commercial lines and $26 million of favorable development in personal lines. There was $8 million from favorable development of catastrophe losses for the three months ended June 30, 2013, compared with $5 million of favorable development of catastrophe losses that occurred for the three months ended June 30, 2012.For the six months ended June 30, 2013, we experienced $102 million of favorable development on prior accident years, including $78 million of favorable development in commercial lines, $22 million of favorable development in personal lines and $2 million favorable development in excess and surplus lines. There was $15 million from favorable development of catastrophe losses for the six months ended June 30, 2013, compared with $27 million of favorable development of catastrophe losses that occurred for the six months ended June 30, 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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