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Investment Securities (Net Realized and Unrealized Gains (Losses) After Tax) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Investments, Debt and Equity Securities [Abstract] |  |  |
Net change in pre-tax unrealized gains (losses) on investments in unconsolidated affiliates | $ (106.4) | $ 62.8 | $ (63.6)
Income taxes | 8.3 | (5.1) | 5.1
Net change in unrealized gains (losses) on investments in unconsolidated affiliates, after tax | (98.1) | 57.7 | (58.5)
Net realized and unrealized foreign currency gains (losses) on investments through OCI | 11.3 | 95.5 | (41.7)
Total investments gains (losses) through accumulated other comprehensive income | (86.8) | 153.2 | (100.2)
Net Realized and Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax | 139.8 | 91.4 | 56.0
Total investment gains (losses) recorded during the period, after-tax | $ 53.0 | $ 244.6 | $ (44.2)

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- Definition The net unrealized gains (losses) from Symetra's fixed maturity portfolio. + References No definition available. + Details
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- Definition Represents total investment gains (losses), after tax, recorded during the period. + References No definition available. + Details
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- Definition Net Realized and Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax + References No definition available. + Details
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- Definition Comprehensive income (loss) attributable to White Mountains' common shareholders. + References No definition available. + Details
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- Definition Adjustment that results from the process of translating unrealized gain (losses) on investments into the reporting currency of the reporting entity, net of tax. + References No definition available. + Details
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- Definition Other Comprehensive Income (Loss) Equity in Unrealized Gains Losses from Investments in Unconsolidated Affiliates + References No definition available. + Details
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- Definition Tax effect on accumulated appreciation or loss in equity in unrealized gains or losses from investments in unconsolidated affiliates. + References No definition available. + Details
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