Municipal Bond Guarantee (Details) $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended
	Jul. 31, 2012 USD ($)	Sep. 30, 2016 USD ($) Contract	Mar. 31, 2016	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) yr Contract	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) Contract
Guarantor Obligations [Line Items]
Pre-tax (loss) income		$ 20.0		$ (86.9)	$ 26.4	$ (89.0)
Net investment income (loss) - surplus note interest		$ 0.0		0.0	$ 0.0	0.0
BAM
Guarantor Obligations [Line Items]
Municipal bond contract | Contract		4,357			4,357		3,103
Insured Financial Obligations, Remaining Weighted Average Contract Period					10 years 11 months		12 years 10 months
Municipal bond outstanding principal		$ 30,470.0			$ 30,470.0		$ 22,556.0
Municipal bond outstanding interest		15,258.1			15,258.1		11,984.4
Municipal bond debt service outstanding		45,728.1			$ 45,728.1		34,540.4
Year of U.S. Treasury Rate | yr					1
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Remainder of Fiscal Year		1.6			$ 1.6
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Second Quarter		1.6			1.6
Financial Guarantee Insurance Contracts, Premium Receivable, Premium Expected to be Collected, Third Quarter		1.6			1.6
Financial Guarantee Insurance Contracts, Premium Receivable, Premium Expected to be Collected, Next Quarter		1.6			1.6
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Next Twelve Months		1.5			1.5
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Two		6.3			6.3
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Three		6.0			6.0
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Five		5.4			5.4
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Four		5.7			5.7
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Six Through Ten		46.0			46.0
Financial Guarantee Insurance Contracts, Unearned Premium Revenue		71.0			71.0		$ 50.2
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			$ 18.4
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		$ (13.7)			$ (30.3)
BAM
Guarantor Obligations [Line Items]
Pre-tax (loss) income		(13.7)		(10.6)	(30.3)	(33.5)
Net investment income (loss) - surplus note interest		(4.5)		(4.0)	(13.4)	(11.9)
HG Re
Guarantor Obligations [Line Items]
Statutory Accounting Practices, Statutory Capital and Surplus, Balance		476.5			476.5
HG Global
Guarantor Obligations [Line Items]
Pre-tax (loss) income		5.2		5.2	18.4	13.8
Net investment income (loss) - surplus note interest		4.5		$ 4.0	13.4	$ 11.9
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			$ 13.4
Derivative, Fixed Interest Rate		3.54%			3.54%		3.15%
Surplus Note | Build America Mutual
Guarantor Obligations [Line Items]
Interest expense		$ 4.5			$ 13.4
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%			8.00%