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Municipal Bond Guarantee Insurance (Details) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2015 USD ($) Contract | Sep. 30, 2015 USD ($) | Jun. 30, 2015 USD ($) | Mar. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) Contract | Sep. 30, 2014 USD ($) | Jun. 30, 2014 USD ($) | Mar. 31, 2014 USD ($) | Dec. 31, 2015 USD ($) Contract | Dec. 31, 2014 USD ($) Contract | Dec. 31, 2013 USD ($) | Dec. 31, 2012 USD ($)
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of par value of policy reinsured | 15.00% |  |  |  |  |  |  |  | 15.00% |  |  |
Pre-tax loss | $ 258.1 | $ (94.6) | $ (9.1) | $ 0.5 | $ (65.7) | $ (35.5) | $ 33.6 | $ 38.6 | $ 154.9 | $ (29.0) | $ 158.6 |
Net investment income (loss) - surplus note interest |  |  |  |  |  |  |  |  | 0.0 | $ 0.0 | 0.0 |
BAM |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Next Quarter | 1.1 |  |  |  |  |  |  |  | 1.1 |  |  |
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Next Twelve Months | 4.4 |  |  |  |  |  |  |  | 4.4 |  |  |
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Two | 4.3 |  |  |  |  |  |  |  | 4.3 |  |  |
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Three | 4.1 |  |  |  |  |  |  |  | 4.1 |  |  |
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Four | 3.8 |  |  |  |  |  |  |  | 3.8 |  |  |
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Five | 3.6 |  |  |  |  |  |  |  | 3.6 |  |  |
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Six Through Ten | 30.0 |  |  |  |  |  |  |  | 30.0 |  |  |
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Two | 1.1 |  |  |  |  |  |  |  | 1.1 |  |  |
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Third Quarter | 1.1 |  |  |  |  |  |  |  | 1.1 |  |  |
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Fourth Quarter | $ 1.1 |  |  |  |  |  |  |  | $ 1.1 |  |  |
Municipal bond contract | Contract | 3,103 |  |  |  | 1,750 |  |  |  | 3,103 | 1,750 |  |
Insured Financial Obligations with Credit Deterioration, Remaining Weighted Average Contract Period |  |  |  |  |  |  |  |  | 12 years 10 months | 12 years 10 months |  |
Municipal bond outstanding principal | $ 22,556.0 |  |  |  | $ 12,362.5 |  |  |  | $ 22,556.0 | $ 12,362.5 |  |
Municipal bond outstanding interest | 11,984.4 |  |  |  | 7,086.9 |  |  |  | 11,984.4 | 7,086.9 |  |
Financial Guarantee Insurance Contracts, Unearned Premium Revenue | $ 50.2 |  |  |  | $ 27.6 |  |  |  | $ 50.2 | $ 27.6 |  |
White Mountains |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Capital contributions |  |  |  |  |  |  |  |  |  |  |  | $ 594.5
HG Global |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Surplus notes |  |  |  |  |  |  |  |  |  |  |  | 503.0
Percentage of par value of policy reinsured | 15.00% |  |  |  |  |  |  |  | 15.00% |  |  |
BAM Management |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Capital contributions |  |  |  |  |  |  |  |  |  |  |  | $ 14.5
Preferred stocks | HG Global |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) | 96.90% |  |  |  |  |  |  |  | 96.90% |  |  |
Common Stock | HG Global |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) | 88.40% |  |  |  | 88.40% |  |  |  | 88.40% | 88.40% |  |
BAM |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Surplus notes | $ 503.0 |  |  |  |  |  |  |  | $ 503.0 |  |  |
Pre-tax loss |  |  |  |  |  |  |  |  | (47.3) | $ (40.5) | (78.6) |
Net investment income (loss) - surplus note interest |  |  |  |  |  |  |  |  | (15.8) | (15.7) | (40.2) |
HG Re |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Statutory capital and surplus | $ 460.8 |  |  |  | $ 449.1 |  |  |  | $ 460.8 | $ 449.1 |  |
Collateral Held in Supplement Trust | 136,200,000 |  |  |  | 120,000,000 |  |  |  | 136,200,000 | 120,000,000 |  |
HG Global |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of par value of policy reinsured | 15.00% |  |  |  |  |  |  |  | 15.00% |  |  |
Pre-tax loss |  |  |  |  |  |  |  |  | $ 17.9 | $ 18.3 | 38.1 |
Net investment income (loss) - surplus note interest |  |  |  |  |  |  |  |  | 15.8 | $ 15.7 | $ 40.2 |
Surplus Note | HG Global |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest Receivable | $ 90.2 |  |  |  |  |  |  |  | $ 90.2 |  |  |

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