| **Reinsurance**                        | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
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| **Reinsurance Disclosures [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| Reinsurance                            | ReinsurancePrimary components of our property casualty operations assumed reinsurance include involuntary and voluntary assumed as well as contracts from our reinsurance assumed operations, known as Cincinnati ReSM. Primary components of our ceded reinsurance include a property per risk treaty, property excess treaty, casualty per occurrence treaty, casualty excess treaty, property catastrophe treaty and catastrophe bonds and retrocessions on our reinsurance assumed operations. 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.Our condensed consolidated statements of income include earned consolidated property casualty insurance premiums on assumed and ceded business: (Dollars in millions)Three months ended March 31, 2016 2015Direct earned premiums$1,119 $1,076Assumed earned premiums15 2Ceded earned premiums(38) (37)Earned premiums$1,096 $1,041     Our condensed consolidated statements of income include incurred consolidated property casualty insurance loss and loss expenses on assumed and ceded business:(Dollars in millions)Three months ended March 31, 2016 2015Direct incurred loss and loss expenses$648 $691Assumed incurred loss and loss expenses10 (1)Ceded incurred loss and loss expenses3 (1)Incurred loss and loss expenses$661 $689     Our ceded incurred results generally vary with our catastrophe experience.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: (Dollars in millions)Three months ended March 31, 2016 2015Direct earned premiums$71 $65Ceded earned premiums(13) (12)Earned premiums$58 $53     Our condensed consolidated statements of income include life insurance contract holders' benefits incurred on ceded business: (Dollars in millions)Three months ended March 31, 2016 2015Direct contract holders' benefits incurred$76 $72Ceded contract holders' benefits incurred(13) (12)Contract holders' benefits incurred$63 $60    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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