Financial Guaranty Insurance Contracts (Details 8) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011 Statements Entities Y RatingCategories Counterparties Securities Agreements Policies D Subsidiaries Markets Companies FiscalQuarters Transactions	Jun. 30, 2010	Jun. 30, 2011 RatingAgency RatingCategories Subsidiaries Counterparties Securities Agreements Policies D Markets Companies FiscalQuarters Entities Transactions	Jun. 30, 2010	Dec. 31, 2010 Policies Securities
Financial guarantee obligations
Number of negotiated agreements	2		2
Threshold days delinquent for which all loan files are requested for review (in days)	60		60
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
Benefit for R&W	1,473,300,000	1,320,800,000	1,473,300,000	1,320,800,000
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
Future Net R&W Benefit at the beginning of the period			1,600,500,000	1,173,100,000
R&W Development and Accretion of Discount	90,900,000	55,900,000	770,900,000	211,900,000
Future Net R&W Benefit at the end of the period	1,473,300,000	1,320,800,000	1,473,300,000	1,320,800,000
Number of Risks as of the end of the period with R&W Benefit Recorded	55		55		46
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
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	90,900,000	55,900,000	770,900,000	211,900,000
U.S. RMBS
Rollforward of Estimated Benefit from Recoveries of Representation and Warranty Breaches, Net of Reinsurance
R&W Recovered			(898,100,000)	(64,200,000)
R&W benefit attributable to transactions covered by the Bank of America Agreement	588,900,000		588,900,000
Gross R&W amounts recovered			1,015,000,000	72,000,000
Alt-A first lien
Total
Benefit for R&W	127,600,000	79,200,000	127,600,000	79,200,000
Rollforward of Estimated Benefit from Recoveries of Representation and Warranty Breaches, Net of Reinsurance
Future Net R&W Benefit at the beginning of the period			81,000,000	64,200,000
R&W Development and Accretion of Discount			46,600,000	15,000,000
Future Net R&W Benefit at the end of the period	127,600,000	79,200,000	127,600,000	79,200,000
Number of Risks as of the end of the period with R&W Benefit Recorded	20		20		17
Outstanding Principal and Interest of Policies with R&W Benefit Recorded as of the end of the period	1,826,700,000		1,826,700,000		1,882,800,000
Breakdown of the development and accretion amount
Total			46,600,000	15,000,000
Total first lien
Financial guarantee obligations
Number of defaulted loan files reviewed	16,200		16,200
Outstanding par of defaulted loans reviewed	4,587,000,000		4,587,000,000
Number of loan files that breached one or more R&W	14,700		14,700
Amount of loans to be repurchased by providers	47,500,000		47,500,000
Number of loans to be repurchased by providers	142		142
Breakdown of the development and accretion amount
Number of transactions insured			21
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
Prime first lien
Total
Benefit for R&W	2,900,000	800,000	2,900,000	800,000
Rollforward of Estimated Benefit from Recoveries of Representation and Warranty Breaches, Net of Reinsurance
Future Net R&W Benefit at the beginning of the period			1,100,000
R&W Development and Accretion of Discount			1,800,000	800,000
Future Net R&W Benefit at the end of the period	2,900,000	800,000	2,900,000	800,000
Number of Risks as of the end of the period with R&W Benefit Recorded	1		1		1
Outstanding Principal and Interest of Policies with R&W Benefit Recorded as of the end of the period	54,500,000		54,500,000		57,100,000
Breakdown of the development and accretion amount
Total			1,800,000	800,000
Option ARM
Total
Benefit for R&W	711,200,000	242,800,000	711,200,000	242,800,000
Rollforward of Estimated Benefit from Recoveries of Representation and Warranty Breaches, Net of Reinsurance
Future Net R&W Benefit at the beginning of the period			309,300,000	203,700,000
R&W Development and Accretion of Discount			449,200,000	52,400,000
R&W Recovered			(47,300,000)	(13,300,000)
Future Net R&W Benefit at the end of the period	711,200,000	242,800,000	711,200,000	242,800,000
Number of Risks as of the end of the period with R&W Benefit Recorded	11		11		10
Outstanding Principal and Interest of Policies with R&W Benefit Recorded as of the end of the period	1,914,800,000		1,914,800,000		1,909,800,000
Breakdown of the development and accretion amount
Total			449,200,000	52,400,000
Subprime
Total
Benefit for R&W	81,500,000		81,500,000
Rollforward of Estimated Benefit from Recoveries of Representation and Warranty Breaches, Net of Reinsurance
Future Net R&W Benefit at the beginning of the period			26,800,000
R&W Development and Accretion of Discount			54,700,000
Future Net R&W Benefit at the end of the period	81,500,000		81,500,000
Number of Risks as of the end of the period with R&W Benefit Recorded	4		4		1
Outstanding Principal and Interest of Policies with R&W Benefit Recorded as of the end of the period	982,700,000		982,700,000		228,700,000
Breakdown of the development and accretion amount
Total			54,700,000
Second lien
Financial guarantee obligations
Number of defaulted loan files reviewed	13,900		13,900
Outstanding par of defaulted loans reviewed	959,000,000		959,000,000
Number of loan files that breached one or more R&W	12,300		12,300
Amount of loans to be repurchased by providers	38,400,000		38,400,000
Number of loans to be repurchased by providers	466		466
Breakdown of the development and accretion amount
Number of transactions insured			8
Closed end second lien and HELOCs
Breakdown of the development and accretion amount
Recovery period, low end of range (in years)	2		2
Recovery period, high end of range (in years)	4		4
CES
Total
Benefit for R&W	239,700,000	123,000,000	239,700,000	123,000,000
Rollforward of Estimated Benefit from Recoveries of Representation and Warranty Breaches, Net of Reinsurance
Future Net R&W Benefit at the beginning of the period			178,200,000	76,500,000
R&W Development and Accretion of Discount			61,500,000	46,500,000
Future Net R&W Benefit at the end of the period	239,700,000	123,000,000	239,700,000	123,000,000
Number of Risks as of the end of the period with R&W Benefit Recorded	4		4		4
Outstanding Principal and Interest of Policies with R&W Benefit Recorded as of the end of the period	396,300,000		396,300,000		444,900,000
Breakdown of the development and accretion amount
Total			61,500,000	46,500,000
HELOCs
Total
Benefit for R&W	310,400,000	875,000,000	310,400,000	875,000,000
Rollforward of Estimated Benefit from Recoveries of Representation and Warranty Breaches, Net of Reinsurance
Future Net R&W Benefit at the beginning of the period			1,004,100,000	828,700,000
R&W Development and Accretion of Discount			157,100,000	97,200,000
R&W Recovered			(850,800,000)	(50,900,000)
Future Net R&W Benefit at the end of the period	310,400,000	875,000,000	310,400,000	875,000,000
Number of Risks as of the end of the period with R&W Benefit Recorded	15		15		13
Outstanding Principal and Interest of Policies with R&W Benefit Recorded as of the end of the period	3,844,900,000		3,844,900,000		2,969,800,000
Breakdown of the development and accretion amount
Total			$ 157,100,000	$ 97,200,000