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Investment Securities Investment Securities (OneBeacon Surplus Notes) (Details) - USD ($) |  | 12 Months Ended
--- | --- | ---
Dec. 23, 2014 | Dec. 31, 2015 | Dec. 31, 2014
Total realized and unrealized gains (losses) |  | $ 226,800,000 | $ (83,300,000)
OneBeacon |  |  |
Gain (loss) on sale of discontinued operations, net of tax | $ (36,100,000) | (49,500,000) | (35,900,000)
Current market rates on repayments | OneBeacon |  |  |
Gain (loss) on sale of discontinued operations, net of tax | (6,800,000) | (15,100,000) | (6,600,000)
Regulatory Approval [Member] | OneBeacon |  |  |
Gain (loss) on sale of discontinued operations, net of tax | (12,600,000) | (24,200,000) | (12,600,000)
Liquidity Adjustment [Member] | OneBeacon |  |  |
Gain (loss) on sale of discontinued operations, net of tax | (16,700,000) | (10,200,000) | (16,700,000)
Fair Value [Member] | OneBeacon |  |  |
Surplus notes | 64,900,000 | 51,500,000 | 65,100,000
Par Value [Member] | OneBeacon |  |  |
Surplus notes | 101,000,000 | 101,000,000 | $ 101,000,000
Seller Priority Surplus Note [Member] | OneBeacon |  |  |
Gain (loss) on sale of discontinued operations, net of tax | (14,000,000) | (19,900,000) |
Seller Priority Surplus Note [Member] | Current market rates on repayments | OneBeacon |  |  |
Gain (loss) on sale of discontinued operations, net of tax | 1,600,000 | (400,000) |
Seller Priority Surplus Note [Member] | Regulatory Approval [Member] | OneBeacon |  |  |
Gain (loss) on sale of discontinued operations, net of tax | (4,600,000) | (11,700,000) |
Seller Priority Surplus Note [Member] | Liquidity Adjustment [Member] | OneBeacon |  |  |
Gain (loss) on sale of discontinued operations, net of tax | (11,000,000) | (7,800,000) |
Seller Priority Surplus Note [Member] | Fair Value [Member] | OneBeacon |  |  |
Surplus notes | 43,900,000 | 38,000,000 |
Seller Priority Surplus Note [Member] | Par Value [Member] | OneBeacon |  |  |
Surplus notes |  | 57,900,000 |
Pari Passu Surplus Note [Member] | OneBeacon |  |  |
Gain (loss) on sale of discontinued operations, net of tax | (22,100,000) | (29,600,000) |
Pari Passu Surplus Note [Member] | Current market rates on repayments | OneBeacon |  |  |
Gain (loss) on sale of discontinued operations, net of tax | (8,400,000) | (14,700,000) |
Pari Passu Surplus Note [Member] | Regulatory Approval [Member] | OneBeacon |  |  |
Gain (loss) on sale of discontinued operations, net of tax | (8,000,000) | (12,500,000) |
Pari Passu Surplus Note [Member] | Liquidity Adjustment [Member] | OneBeacon |  |  |
Gain (loss) on sale of discontinued operations, net of tax | (5,700,000) | (2,400,000) |
Pari Passu Surplus Note [Member] | Fair Value [Member] | OneBeacon |  |  |
Surplus notes | 21,000,000 | 13,500,000 |
Pari Passu Surplus Note [Member] | Par Value [Member] | OneBeacon |  |  |
Surplus notes | $ 43,100,000 | 43,100,000 |
Symetra |  |  |
Total realized and unrealized gains (losses) |  | $ 258,800,000.0 |
Surplus Note |  |  |
RBC Score |  | 250.00% |

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