Financial Guaranty Contracts Accounted for as Insurance (Details 4) (USD $)	6 Months Ended
	Jun. 30, 2011 RatingCategories Subsidiaries Securities Policies D Companies Agreements Markets Transactions FiscalQuarters Counterparties Entities	Mar. 31, 2011	Dec. 31, 2010	Jun. 30, 2011 Total first lien Financial Guaranty	Dec. 31, 2010 Total first lien Financial Guaranty	Jun. 30, 2010 Total first lien Financial Guaranty	Dec. 31, 2009 Total first lien Financial Guaranty	Jun. 30, 2011 Second lien Financial Guaranty	Dec. 31, 2010 Second lien Financial Guaranty	Jun. 30, 2010 Second lien Financial Guaranty	Dec. 31, 2009 Second lien Financial Guaranty	Jun. 30, 2011 Financial Guaranty	Dec. 31, 2010 Financial Guaranty	Jun. 30, 2010 Financial Guaranty	Dec. 31, 2009 Financial Guaranty	Jun. 30, 2011 Other	Dec. 31, 2010 Other	Jun. 30, 2011 Second lien Securities Loans Transactions D
Reconciliation of Expected Loss to be Paid and Net Expected Loss to be Expensed
Net expected loss to be paid				$ 599,200,000	$ 909,900,000	$ 906,900,000	$ 827,100,000	$ (133,000,000)	$ (749,100,000)	$ (374,700,000)	$ (33,600,000)	$ 713,000,000	$ 394,800,000	$ 753,300,000	$ 1,027,000,000	$ 2,100,000	$ 2,100,000
Less: net expected loss to be paid for FG VIEs												(5,600,000)	49,200,000
Total												718,600,000	345,600,000
Contra-paid, net												88,600,000	121,300,000
Salvage and subrogation recoverable, net												271,900,000	903,000,000
Loss and LAE reserve, net	(492,100,000)		(540,700,000)									(490,000,000)	(538,600,000)			2,100,000	2,100,000
Net expected loss to be expensed												589,100,000	831,300,000
Gross salvage and subrogation amounts	307,147,000		1,032,369,000									307,100,000	1,032,400,000
Salvage and subrogation ceded amounts	35,200,000		129,400,000									35,200,000	129,400,000
Net expected loss to be expensed related to consolidated financial guaranty VIEs	$ 260,300,000		$ 211,900,000
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)	0.65	0.65	0.60