|**Income Taxes**                       | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
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|**Income Tax Disclosure [Abstract]**   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Income Taxes                           | INCOME TAXESAs ofJune 30, 2014, andDecember 31, 2013, we had no liability for unrecognized tax benefits.The differences between the35percent statutory income tax rate and our effective income tax rate were as follows:(In millions)Three months ended June 30,Six months ended June 30,2014201320142013Tax at statutory rate$3735.0%$5235.0%$7935.0%$12835.0%Increase (decrease) resulting from:Tax-exempt income from municipal bonds(8)(7.5)(9)(6.1)(16)(7.1)(16)(4.4)Dividend received exclusion(7)(6.5)(6)(4.2)(14)(6.2)(12)(3.3)Other10.511.020.910.4Provision for income taxes$2321.5%$3825.7%$5122.6%$10127.7%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 immaterial changes in the amount of permanent book-tax differences.
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|(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 for income taxes             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
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