Municipal Bond Guarantee (Details) $ in Millions	1 Months Ended	3 Months Ended		12 Months Ended
	Jul. 31, 2012 USD ($)	Mar. 31, 2016 USD ($) yr Contract	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) Contract
Guarantor Obligations [Line Items]
Pre-tax (loss) income		$ 11.5	$ 0.5
Net investment income (loss) - surplus note interest		$ 0.0	0.0
BAM
Guarantor Obligations [Line Items]
Municipal bond contract | Contract		3,422		3,103
Insured Financial Obligations, Remaining Weighted Average Contract Period		12 years 8 months		12 years 10 months
Municipal bond outstanding principal		$ 24,641.6		$ 22,556.0
Municipal bond outstanding interest		12,711.9		11,984.4
Municipal bond debt service outstanding		37,353.5		34,540.4
Financial Guarantee Insurance Contracts, Unearned Premium Revenue		$ 55.8		$ 50.2
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		$ 7.3
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		$ (7.6)	(8.8)
HG Re
Guarantor Obligations [Line Items]
Statutory Accounting Practices, Statutory Capital and Surplus, Balance		467.2
HG Global
Guarantor Obligations [Line Items]
Pre-tax (loss) income		7.3
Net investment income (loss) - surplus note interest		$ 4.5
HG Global | HG Global
Guarantor Obligations [Line Items]
Pre-tax (loss) income			5.5
Net investment income (loss) - surplus note interest			4.0
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		$ 4.5
Derivative, Fixed Interest Rate		3.54%		3.15%
Surplus Note | Build America Mutual
Guarantor Obligations [Line Items]
Interest income (expense), surplus notes		$ 4.5	$ 4.0
Combination One [Member] | Surplus Note | BAM
Guarantor Obligations [Line Items]
Number of years of change in interest rate | yr		5
Combination Two [Member] | 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%