Municipal Bond Guarantee (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended	1 Months Ended
	Mar. 31, 2015 Y Contract	Mar. 31, 2014	Dec. 31, 2014 Contract	Jul. 31, 2012
BAM
Guarantor Obligations [Line Items]
Municipal bond contract	2,029		1,750
Insured Financial Obligations, Remaining Weighted Average Contract Period	12 years 10 months 0 days		12 years 10 months 0 days
Municipal bond outstanding principal	$ 14,421.6		$ 12,362.5
Municipal bond outstanding interest	8,044.7		7,086.9
Municipal bond debt service outstanding	22,466.3		19,449.4
Interest income (expense), surplus notes	4.0	3.9
Financial Guarantee Insurance Contracts, Unearned Premium Revenue	31.2		27.6
Year of U.S. Treasury Rate	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	5.4	4.6
HG Global | Preferred Stock
Guarantor Obligations [Line Items]
Ownership interest (as a percent)	96.90%
HG Global | Common Stock
Guarantor Obligations [Line Items]
Ownership interest (as a percent)	88.40%
Build America Mutual
Guarantor Obligations [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Domestic	(8.7)	(8.6)
Interest income (expense), surplus notes	(4.0)	(3.9)
HG Re
Guarantor Obligations [Line Items]
Statutory Accounting Practices, Statutory Capital and Surplus, Balance	453.0
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%		3.13%
Combination One | Surplus Note | BAM
Guarantor Obligations [Line Items]
Number of years of change in interest rate	5
Combination Two | Surplus Note | BAM
Guarantor Obligations [Line Items]
Number of years of change in interest rate	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%