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Municipal Bond Guarantee (Details) $ in Millions | 1 Months Ended | 3 Months Ended | 6 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | ---
Jul. 31, 2012 USD ($) | Sep. 30, 2015 USD ($) Contract | Sep. 30, 2014 USD ($) | Jun. 30, 2015 | Sep. 30, 2015 USD ($) Contract yr | Sep. 30, 2014 USD ($) | Dec. 31, 2014 USD ($) Contract
Guarantor Obligations [Line Items] |  |  |  |  |  |  |
Pre-tax (loss) income |  | $ (94.6) | $ (35.5) |  | $ (103.2) | $ 36.7 |
Net investment income (loss) - surplus note interest |  | $ 0.0 | 0.0 |  | $ 0.0 | 0.0 |
BAM |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |
Municipal bond contract | Contract |  | 2,733 |  |  | 2,733 |  | 1,750
Insured Financial Obligations, Remaining Weighted Average Contract Period |  |  |  |  | 12 years 8 months |  | 12 years 10 months
Municipal bond outstanding principal |  | $ 19,841.0 |  |  | $ 19,841.0 |  | $ 12,362.5
Municipal bond outstanding interest |  | 10,574.3 |  |  | 10,574.3 |  | 7,086.9
Municipal bond debt service outstanding |  | 30,415.3 |  |  | 30,415.3 |  | 19,449.4
Financial Guarantee Insurance Contracts, Unearned Premium Revenue |  | 43.2 |  |  | $ 43.2 |  | $ 27.6
Year of U.S. Treasury Rate | yr |  |  |  |  | 1 |  |
HG Global |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |
Partners Capital Contribution | $ 594.5 |  |  |  |  |  |
Surplus Notes | 503.0 |  |  |  |  |  |
Income (Loss) from Continuing Operations before Income Taxes, Domestic |  | $ 5.2 |  |  | $ 13.8 |  |
HG Global | Preferred Stock |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |
Ownership interest (as a percent) |  | 96.90% |  |  | 96.90% |  |
HG Global | Common Stock |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |
Ownership interest (as a percent) |  | 88.40% |  |  | 88.40% |  |
Build America Mutual |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |
Income (Loss) from Continuing Operations before Income Taxes, Domestic |  | $ (10.6) | (13.1) |  | $ (33.5) | (29.7) |
HG Re |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |
Statutory Accounting Practices, Statutory Capital and Surplus, Balance |  | 458.3 |  |  | 458.3 |  |
HG Global |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |
Pre-tax (loss) income |  | 5.2 |  |  | 13.8 |  |
Net investment income (loss) - surplus note interest |  | 4.0 |  |  | 11.9 |  |
HG Global | HG Global |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |
Pre-tax (loss) income |  |  | 3.8 |  |  | 13.4 |
Net investment income (loss) - surplus note interest |  |  | 3.9 |  |  | 11.8 |
BAM Management |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |
Partners Capital Contribution | $ 14.5 |  |  |  |  |  |
Surplus Note | BAM |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |
Basis points |  |  |  | 3.00% |  |  |
Interest Income, Other |  | $ 4.0 |  |  | $ 11.9 |  |
Derivative, Fixed Interest Rate |  | 3.15% |  |  | 3.15% |  | 3.13%
Surplus Note | Build America Mutual |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |
Interest income (expense), surplus notes |  | $ 4.0 | $ 3.9 |  | $ 11.9 | $ 11.8 |
Combination One | Surplus Note | BAM |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |
Number of years of change in interest rate | yr |  |  |  |  | 5 |  |
Combination Two | Surplus Note | BAM |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |
Number of years of change in interest rate | yr |  |  |  |  | 3 |  |
Financial Guarantee [Member] |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |
Percentage of par value of policy reinsured |  |  |  |  | 15.00% |  |
Fixed interest rate [Member] | Surplus Note | BAM |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |
Derivative, Fixed Interest Rate |  | 8.00% |  |  | 8.00% |  |

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