|**Income Taxes**                       | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
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|**Income Tax Disclosure [Abstract]**   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Income Taxes                           | INCOME TAXESAs ofJune 30, 2013, andDecember 31, 2012, we had no liability for unrecognized tax benefits. Details about our liability for unrecognized tax benefits are found in our 2012 Annual Report on Form 10-K, Item 8, Note 11, Income Taxes, Page 129.The differences between the35percent statutory income tax rate and our effective income tax rate were as follows:(Dollars in millions)Three months ended June 30,Six months ended June 30,2013201220132012Tax at statutory rate$5235.0%$1035.0%$12835.0%$4935.0%Increase (decrease) resulting from:Tax-exempt income from municipal bonds(9)(6.1)(8)(27.6)(16)(4.4)(17)(12.1)Dividend received exclusion(6)(4.2)(6)(20.7)(12)(3.3)(11)(7.8)Other11.013.010.421.2Provision (benefit) for income taxes$3825.7%$(3)(10.3)%$10127.7%$2316.3%The change in our effective tax rate was primarily due to changes in pretax income from underwriting results and realized investment gains and losses, compared with unchanged levels of permanent book-tax differences.
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|(Dollars in millions)                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
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|Tax at statutory rate                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Increase (decrease) resulting from:    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Tax-exempt income from municipal bonds |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Dividend received exclusion            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Other                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Provision (benefit) for income taxes   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              

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