Municipal Bond Guarantee (Details) $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 31, 2012 USD ($)	Jun. 30, 2015 USD ($) Contract	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) yr Contract	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) Contract
BAM
Guarantor Obligations [Line Items]
Municipal bond contract | Contract		2,436		2,436		1,750
Insured Financial Obligations, Remaining Weighted Average Contract Period				12 years 8 months		12 years 10 months
Municipal bond outstanding principal		$ 17,766.6		$ 17,766.6		$ 12,362.5
Municipal bond outstanding interest		9,588.1		9,588.1		7,086.9
Municipal bond debt service outstanding		27,354.7		27,354.7		19,449.4
Financial Guarantee Insurance Contracts, Unearned Premium Revenue		37.1		$ 37.1		$ 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		$ 3.1	$ 5.0	$ 8.6	$ 9.6
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		$ (14.1)	(8.0)	$ (22.9)	(16.6)
HG Re
Guarantor Obligations [Line Items]
Statutory Accounting Practices, Statutory Capital and Surplus, Balance		$ 454.6		$ 454.6
BAM Management
Guarantor Obligations [Line Items]
Partners Capital Contribution	$ 14.5
Surplus Note | BAM
Guarantor Obligations [Line Items]
Basis points				3.00%
Derivative, Fixed Interest Rate		3.15%		3.15%		3.13%
Surplus Note | Build America Mutual
Guarantor Obligations [Line Items]
Interest income (expense), surplus notes		$ 3.9	$ 4.0	$ 7.9	$ 7.9
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%