Financial Guaranty Insurance Contracts (Details 12) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal									$ 554,600,000	$ 478,100,000	$ 393,800,000
Effect of consolidating FG VIEs									(92,700,000)	(65,900,000)
Total loss and LAE	148,600,000	214,900,000	123,900,000	(25,500,000)	104,800,000	110,800,000	85,700,000	110,900,000	461,890,000	412,161,000	393,800,000
Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal									554,600,000	477,900,000	381,700,000
Financial Guaranty | U.S. RMBS
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal									388,600,000	381,400,000	279,100,000
Financial Guaranty | Total first lien
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal									216,200,000	396,600,000	77,200,000
Financial Guaranty | Prime first lien
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal									100,000	900,000
Financial Guaranty | Alt-A first lien
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal									52,600,000	37,400,000	21,100,000
Financial Guaranty | Option ARM
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal									202,600,000	272,400,000	43,000,000
Financial Guaranty | Subprime
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal									(39,100,000)	85,900,000	13,100,000
Financial Guaranty | Second lien
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal									172,400,000	(15,200,000)	201,900,000
Financial Guaranty | CES
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal									1,000,000	5,200,000	47,800,000
Financial Guaranty | HELOCs
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal									171,400,000	(20,400,000)	154,100,000
Financial Guaranty | Structured Finance
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal									117,600,000	63,600,000	31,400,000
Financial Guaranty | Public finance
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal									48,400,000	32,900,000	71,200,000
Other
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal										$ 200,000	$ 12,100,000