| **Reinsurance**                        | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
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| **Reinsurance Disclosures [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
| Reinsurance                            | REINSURANCEReinsurance mitigates the risk of highly uncertain exposures and limits the maximum net loss that can arise from large risks or risks concentrated in areas of exposure. Management's decisions about the appropriate level of risk retention are affected by various factors, including changes in our underwriting practices, capacity to retain risks and reinsurance market conditions.Primary components of our property casualty reinsurance program include a property per risk treaty, property excess treaty, casualty per occurrence treaty, casualty excess treaty, property catastrophe treaty and catastrophe bonds. Our condensed consolidated statements of income include earned consolidated property casualty insurance premiums on assumed and ceded business: (In millions) Three months ended March 31,  2014 2013Direct earned premiums $1,019 $935Assumed earned premiums 3 2Ceded earned premiums (43) (48)Net earned premiums $979 $889      Our condensed consolidated statements of income include incurred consolidated property casualty insurance loss and loss expenses on assumed and ceded business:(In millions) Three months ended March 31,  2014 2013Direct incurred loss and loss expenses $677 $535Assumed incurred loss and loss expenses 2 2Ceded incurred loss and loss expenses (3) (13)Net incurred loss and loss expenses $676 $524      Our life insurance company purchases reinsurance for protection of a portion of the risk that is written. Primary components of our life reinsurance program include individual mortality coverage and aggregate catastrophe and accidental death coverage in excess of certain deductibles. Our condensed consolidated statements of income include earned life insurance premiums on ceded business: (In millions) Three months ended March 31,  2014 2013Direct earned premiums $62 $56Ceded earned premiums (14) (14)Net earned premiums $48 $42      Our condensed consolidated statements of income include life insurance policyholders’ benefits incurred on ceded business: (In millions) Three months ended March 31,  2014 2013Direct policyholders' benefits incurred $80 $64Ceded policyholders' benefits incurred (24) (20)Net policyholders' benefits incurred $56 $44     The ceded benefits incurred can vary depending on the type of life insurance policy held and the year the policy was sold. |

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| - Definition
The entire disclosure pertaining to the existence, magnitude and information about insurance that has been ceded to or assumed from another insurance company, including the methodologies and assumptions used in determining recorded amounts.
+ References
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