Financial Guaranty Insurance Contracts (Details 9) (USD $)	3 Months Ended							3 Months Ended			3 Months Ended				3 Months Ended			3 Months Ended			3 Months Ended			3 Months Ended				3 Months Ended			3 Months Ended
	Mar. 31, 2012 Agreement	Mar. 31, 2011 Transaction	Dec. 31, 2011	Mar. 31, 2012 Bank of America agreement	Apr. 14, 2011 Bank of America agreement Agreement	Mar. 31, 2011 Bank of America agreement	May 08, 2012 Deutsche Bank Agreement Agreement	Mar. 31, 2012 U.S. RMBS policy	Mar. 31, 2011 U.S. RMBS	Dec. 31, 2011 U.S. RMBS policy	Mar. 31, 2012 Alt-A first lien policy	Mar. 31, 2011 Alt-A first lien	Dec. 31, 2011 Alt-A first lien policy	Mar. 31, 2012 Total first lien loan	Mar. 31, 2012 Total first lien Bank of America agreement Transaction	Mar. 31, 2012 Total first lien Bank of America agreement AGM and AGC	Mar. 31, 2012 Total first lien Bank of America agreement Maximum	Mar. 31, 2012 Prime first lien policy	Mar. 31, 2011 Prime first lien	Dec. 31, 2011 Prime first lien policy	Mar. 31, 2012 Option ARM policy	Mar. 31, 2011 Option ARM	Dec. 31, 2011 Option ARM policy	Mar. 31, 2012 Subprime policy	Mar. 31, 2011 Subprime	Dec. 31, 2011 Subprime policy	Mar. 31, 2012 Second lien loan	Mar. 31, 2012 CES policy	Mar. 31, 2011 CES	Dec. 31, 2011 CES policy	Mar. 31, 2012 HELOCs policy	Mar. 31, 2011 HELOCs	Dec. 31, 2011 HELOCs policy
Financial guarantee obligations
Number of negotiated agreements	3				1		1
Number of defaulted loan files reviewed														20,300													16,500
Outstanding par of defaulted loans reviewed														$ 5,900,000,000													$ 1,100,000,000
Number of loan files that breached one or more R&W														18,100													15,300
Threshold days delinquent for which all loan files are requested for review (in days)	60 days
Amount of loans to be repurchased by providers														74,800,000													41,800,000
Number of loans to be repurchased by providers														285													514
Salvage and subrogation recoverable
For all Financial Guaranty Insurance Contracts	389,100,000		401,800,000
Effect of Consolidating FG VIEs	(216,400,000)		(197,300,000)
Reported on Balance Sheet	172,700,000		204,500,000
Loss and LAE reserve
For all Financial Guaranty Insurance Contracts	818,500,000		857,500,000
Effect of Consolidating FG VIEs	(74,500,000)		(74,600,000)
Reported on Balance Sheet	744,000,000		782,900,000
Unearned premium reserve
For all Financial Guaranty Insurance Contracts	190,000,000		175,500,000
Effect of Consolidating FG VIEs	(56,200,000)		(49,900,000)
Reported on Balance Sheet	133,800,000		125,600,000
Total
Benefit for R&W	1,397,600,000	2,221,000,000		482,100,000		1,324,300,000					211,100,000	120,700,000				487,200,000		3,600,000	2,300,000		723,800,000	619,000,000		96,400,000	81,100,000			221,600,000	273,200,000		141,100,000	1,124,700,000
Effect of Consolidating FG VIEs	(347,100,000)		(321,800,000)
Reported on Balance Sheet	1,050,500,000		1,113,000,000
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	1,434,800,000	1,600,500,000		482,100,000		1,324,300,000					202,700,000	81,000,000						3,000,000	1,100,000		713,900,000	309,300,000		101,500,000	26,800,000			223,800,000	178,200,000		189,900,000	1,004,100,000
R&W Development and Accretion of Discount	32,400,000	680,000,000									9,400,000	39,700,000						600,000	1,200,000		27,500,000	335,300,000		(5,100,000)	54,300,000			(2,200,000)	95,000,000		2,200,000	154,500,000
R&W Recovered	(69,600,000)	(59,500,000)									(1,000,000)					(76,300,000)					(17,600,000)	(25,600,000)									(51,000,000)	(33,900,000)
Future Net R&W Benefit at the end of the period	1,397,600,000	2,221,000,000		482,100,000		1,324,300,000					211,100,000	120,700,000				487,200,000		3,600,000	2,300,000		723,800,000	619,000,000		96,400,000	81,100,000			221,600,000	273,200,000		141,100,000	1,124,700,000
Gross R&W amounts recovered								77,200,000	64,200,000
Number of Risks as of the end of the period with R&W Benefit Recorded (in policies)								49		59	21		22					1		1	11		12	5		5		4		4	7		15
Debt Service of Policies with R&W Benefit Recorded as of the end of the period								4,867,800,000		7,479,900,000	1,670,000,000		1,732,600,000					40,500,000		41,900,000	1,337,600,000		1,459,700,000	825,700,000		905,800,000		262,800,000		361,400,000	731,200,000		2,978,500,000
Breakdown of the development and accretion amount
Inclusion of new deals with breaches of R&W during period		107,100,000
Change in recovery assumptions as the result of additional file review and recovery success	79,700,000	198,400,000
Estimated increase (decrease) in defaults that will result in additional breaches	(51,300,000)	39,800,000
Results of settlements		334,100,000
Accretion of discount on balance	4,000,000	600,000
Total	32,400,000	680,000,000									9,400,000	39,700,000						600,000	1,200,000		27,500,000	335,300,000		(5,100,000)	54,300,000			(2,200,000)	95,000,000		2,200,000	154,500,000
Number of additional transactions resulting in development		4
Additional information related to Representations and Warranties
Number of transactions insured executed as financial guarantees															20
Cumulative collateral losses															2,100,000,000		6,600,000,000
Cumulative projected collateral losses															4,800,000,000
Gross expected losses before considering R&W recoveries															626,500,000
Gross expected losses after considering R&W recoveries															125,300,000
Recovery payments received	69,600,000	59,500,000									1,000,000					76,300,000					17,600,000	25,600,000									51,000,000	33,900,000
Additional invoices for claims paid																13,900,000
Eligible assets in trust for payment of reimbursement															1,000,000,000
Estimated benefit from loan repurchases relating breaches of R&W	$ 1,400,000,000