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Income Taxes (Tax Examinations) (Details) - USD ($) $ in Millions | Mar. 31, 2016 | Dec. 31, 2015 | Mar. 31, 2014
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Income Tax Examination [Line Items] |  |  |
Unrecognized tax benefit recognition including interest and penalties, if recognized, would effect income tax expense |  | $ 13.6 | $ 5.0
Tax Assessment Year 2005 to 2006 [Member] | IRS |  |  |
Income Tax Examination [Line Items] |  |  |
Tax Examination |  | 3.3 |
Tax Assessment Year 2007 to 2009 [Member] | IRS |  |  |
Income Tax Examination [Line Items] |  |  |
Tax Examination |  | 4.0 |
Income Tax Examination, Increase (Decrease) in Liability from Prior Year, Dissallowed |  | 2.7 |
OneBeacon |  |  |
Income Tax Examination [Line Items] |  |  |
Income Tax Examination, Liability (Refund) Adjustment from Settlement with Taxing Authority |  | $ 1.1 |
Scenario, Forecast [Member] |  |  |
Income Tax Examination [Line Items] |  |  |
Unrecognized tax benefit recognition including interest and penalties, if recognized, would effect income tax expense | $ 12.0 |  |

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- Definition The amount of the additional liability or refund received or expected based on a final settlement with a taxing authority. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319 + Details
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