Financial Guaranty Insurance Contracts (Details 4) (USD $)	9 Months Ended
	Sep. 30, 2011 subsidiary statement ratingcategory security Y segment entity agreement market company policy D transaction counterparty	Jun. 30, 2011	Dec. 31, 2010	Sep. 30, 2010	Sep. 30, 2011 Total first lien Financial Guaranty	Jun. 30, 2011 Total first lien Financial Guaranty	Dec. 31, 2010 Total first lien Financial Guaranty	Sep. 30, 2010 Total first lien Financial Guaranty	Jun. 30, 2010 Total first lien Financial Guaranty	Dec. 31, 2009 Total first lien Financial Guaranty	Sep. 30, 2011 Second lien Financial Guaranty	Jun. 30, 2011 Second lien Financial Guaranty	Dec. 31, 2010 Second lien Financial Guaranty	Sep. 30, 2010 Second lien Financial Guaranty	Jun. 30, 2010 Second lien Financial Guaranty	Dec. 31, 2009 Second lien Financial Guaranty	Sep. 30, 2011 Financial Guaranty	Jun. 30, 2011 Financial Guaranty	Dec. 31, 2010 Financial Guaranty	Sep. 30, 2010 Financial Guaranty	Jun. 30, 2010 Financial Guaranty	Dec. 31, 2009 Financial Guaranty	Sep. 30, 2011 Second lien loan D security
Reconciliation of Expected Loss to be Paid and Net Expected Loss to be Expensed
Net expected loss to be paid					$ 590,100,000	$ 599,200,000	$ 909,900,000	$ 881,800,000	$ 906,900,000	$ 827,100,000	$ (119,000,000)	$ (133,000,000)	$ (749,100,000)	$ (521,000,000)	$ (374,700,000)	$ (7,300,000)	$ 773,400,000	$ 713,000,000	$ 408,800,000	$ 589,300,000	$ 766,900,000	$ 1,066,400,000
Less: net expected loss to be paid for FG VIEs																	(34,200,000)		49,200,000	(30,500,000)
Total																	807,600,000		359,600,000	619,800,000
Contra-paid, net																	82,100,000		121,300,000	183,500,000
Salvage and subrogation recoverable, net																	314,600,000			727,600,000
Loss and LAE reserve, net	(622,700,000)		(552,100,000)														(620,800,000)			(457,900,000)
Total present value basis																	583,500,000			1,073,000,000
Gross salvage and subrogation amounts	360,161,000		1,032,369,000	824,800,000
Salvage and subrogation ceded amounts	45,600,000		129,400,000	97,200,000
Reserves for other runoff lines of business	1,900,000	2,100,000	2,100,000
Net expected loss to be expensed related to consolidated financial guaranty VIEs	$ 240,000,000			$ 110,000,000
Number of delinquency category from which liquidation rates may be derived	1
Number of types of RMBS insured																							2
Assumed initial loss severities for subprime transactions (as a percent)	65.00%	65.00%	60.00%