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Summary of Significant Accounting Policies Summary of Significant Accounting Policies - LIHC (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2015 | Sep. 30, 2015 | Jun. 30, 2015 | Mar. 31, 2015 | Dec. 31, 2014 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Item Effected [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net investment income |  |  |  |  |  |  |  |  | $ 60.8 | $ 59.5 | $ 59.8
Income Tax Expense (Benefit) | $ (1.5) | $ (1.6) | $ (2.2) | $ 4.6 | $ (26.2) | $ (4.7) | $ 7.1 | $ 9.0 | $ (0.7) | (14.8) | 32.6
OneBeacon Ltd. |  |  |  |  |  |  |  |  |  |  |
Item Effected [Line Items] |  |  |  |  |  |  |  |  |  |  |
Cumulative Effect on Retained Earnings, Net of Tax |  |  |  |  |  |  |  |  |  | 0.9 | 0.4
Accounting Standards Update 2014-01 [Member] | Restatement Adjustment [Member] | OneBeacon Ltd. |  |  |  |  |  |  |  |  |  |  |
Item Effected [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net investment income |  |  |  |  |  |  |  |  |  | 1.7 | 1.9
Income Tax Expense (Benefit) |  |  |  |  |  |  |  |  |  | $ 2.3 | $ 2.2

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