Financial Guaranty Contracts Accounted for as Insurance (Details 8) (USD $)	3 Months Ended		6 Months Ended			6 Months Ended				6 Months Ended				6 Months Ended					6 Months Ended					6 Months Ended
	Jun. 30, 2011 Entities RatingCategories Y Statements Securities Policies D Companies Agreements Markets Subsidiaries Transactions FiscalQuarters Counterparties	Jun. 30, 2010	Jun. 30, 2011 RatingCategories Subsidiaries Securities Policies D Companies Agreements Markets Transactions FiscalQuarters Counterparties Entities	Jun. 30, 2010	Dec. 31, 2010 Securities Policies	Jun. 30, 2011 U.S. RMBS	Jun. 30, 2010 U.S. RMBS	Jun. 30, 2011 Alt-A first lien Policies	Dec. 31, 2010 Alt-A first lien Policies	Jun. 30, 2011 Total first lien M Y Transactions Loans	Mar. 31, 2011 Total first lien Loans	Jun. 30, 2011 Prime first lien Policies	Dec. 31, 2010 Prime first lien Policies	Jun. 30, 2011 Option ARM Policies	Jun. 30, 2010 Option ARM	Dec. 31, 2010 Option ARM Policies	Jun. 30, 2011 Subprime Policies	Dec. 31, 2010 Subprime Policies	Jun. 30, 2011 Second lien M D RatingCategories RateCurves Transactions Securities Loans	Mar. 31, 2011 Second lien Loans	Jun. 30, 2011 Closed end second lien and HELOCs Y	Jun. 30, 2011 CES Policies M	Dec. 31, 2010 CES M Policies	Jun. 30, 2011 HELOCs M Policies	Jun. 30, 2010 HELOCs	Dec. 31, 2010 HELOCs Policies M
Financial guarantee obligations
Number of negotiated agreements	2		2
Number of defaulted loan files reviewed											17,800									13,900
Outstanding par of defaulted loans reviewed											$ 5,180,000,000									$ 959,000,000
Number of loan files that breached one or more R&W																				12,300
Threshold days delinquent for which all loan files are requested for review (in days)	60		60
Amount of loans to be repurchased by providers										47,500,000									38,400,000
Number of loans to be repurchased by providers										142									466
Salvage and subrogation recoverable
Benefit for R&W	400,000,000		400,000,000		900,000,000
Effect of Consolidating FG VIEs	(200,000,000)		(200,000,000)		(100,000,000)
Reported on Balance Sheet	200,000,000		200,000,000		800,000,000
Loss and LAE reserve
Benefit for R&W	900,000,000		900,000,000		500,000,000
Effect of Consolidating FG VIEs	(100,000,000)		(100,000,000)		(100,000,000)
Reported on Balance Sheet	800,000,000		800,000,000		400,000,000
Unearned premium reserve
Benefit for R&W	200,000,000		200,000,000		200,000,000
Reported on Balance Sheet	200,000,000		200,000,000		200,000,000
Total
Effect of Consolidating FG VIEs	(300,000,000)		(300,000,000)		(200,000,000)
Reported on Balance Sheet	1,200,000,000		1,200,000,000		1,400,000,000
Rollforward of Estimated Benefit from Recoveries of Representation and Warranty Breaches, Net of Reinsurance
R&W Development and Accretion of Discount						55,900,000
R&W Recovered						(898,100,000)	(64,200,000)							(47,300,000)	(13,300,000)									(850,800,000)	(50,900,000)
R&W benefit attributable to transactions covered by the Bank of America Agreement						588,900,000
Gross R&W amounts recovered						1,015,000,000	72,000,000
Number of Risks as of the end of the period with R&W Benefit Recorded	55		55		46			20	17			1	1	11		10	4	1				4	4	15		13
Outstanding Principal and Interest of Policies with R&W Benefit Recorded as of the end of the period	9,019,900,000		9,019,900,000		7,493,100,000			1,826,700,000	1,882,800,000			54,500,000	57,100,000	1,914,800,000		1,909,800,000	982,700,000	228,700,000				396,300,000	444,900,000	3,844,900,000		2,969,800,000
Breakdown of the development and accretion amount
Inclusion of new deals with breaches of R&W during period			107,100,000	62,400,000
Change in recovery assumptions as the result of additional file review and recovery success		35,500,000	198,400,000	65,300,000
Estimated increase (decrease) in defaults that will result in additional breaches	(5,800,000)	18,400,000	34,000,000	82,100,000
Results of Bank of America Agreement	95,600,000		429,700,000
Accretion of discount on balance	1,100,000	2,000,000	1,700,000	2,100,000
Total						55,900,000
Recovery period, low end of range (in years)																					2
Recovery period, high end of range (in years)																					4
Number of transactions insured										21									8
Cumulative collateral losses										1,600,000,000
Cumulative projected collateral losses										4,840,000,000
Gross expected losses before considering R&W recoveries from Bank of America										630,900,000
Gross expected losses after considering R&W recoveries from Bank of America										126,800,000
Payment remibursed by Bank of America										$ 14,900,000