Financial Guaranty Insurance Contracts (Details 11) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	$ 252,800,000	$ 121,000,000	$ 418,800,000	$ 351,800,000
Effect of consolidating FG VIEs	(37,900,000)	(10,200,000)	(105,500,000)	(44,400,000)
Total loss and LAE	214,991,000	110,772,000	313,324,000	307,394,000
Net Losses Paid (Recovered) on Financial Guaranty Insurance Contracts
Subtotal	152,200,000	243,700,000	(233,900,000)	719,600,000
Effect of consolidating FG VIEs	(47,500,000)	(37,000,000)	(59,700,000)	(95,900,000)
Total	104,700,000	206,700,000	(293,600,000)	623,700,000
Public finance | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	(5,200,000)	(600,000)	(16,900,000)	10,300,000
Net Losses Paid (Recovered) on Financial Guaranty Insurance Contracts
Subtotal	30,200,000	22,900,000	39,400,000	57,100,000
Total	30,200,000	22,900,000	39,400,000	57,100,000
Total first lien | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	132,900,000	84,500,000	197,600,000	240,000,000
Net Losses Paid (Recovered) on Financial Guaranty Insurance Contracts
Subtotal	91,900,000	69,100,000	314,600,000	149,500,000
Total	91,900,000	69,100,000	314,600,000	149,500,000
U.S. RMBS | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	174,000,000	106,500,000	320,300,000	289,700,000
Net Losses Paid (Recovered) on Financial Guaranty Insurance Contracts
Subtotal	117,300,000	218,700,000	(281,000,000)	654,800,000
Total	117,300,000	218,700,000	(281,000,000)	654,800,000
Prime first lien | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	(400,000)	500,000	700,000	500,000
Alt-A first lien | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	25,200,000	8,800,000	52,600,000	22,300,000
Net Losses Paid (Recovered) on Financial Guaranty Insurance Contracts
Subtotal	16,600,000	14,100,000	55,200,000	43,100,000
Total	16,600,000	14,100,000	55,200,000	43,100,000
Option ARM | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	92,400,000	65,300,000	133,700,000	166,300,000
Net Losses Paid (Recovered) on Financial Guaranty Insurance Contracts
Subtotal	74,500,000	54,300,000	242,900,000	103,400,000
Total	74,500,000	54,300,000	242,900,000	103,400,000
Subprime | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	15,700,000	9,900,000	10,600,000	50,900,000
Net Losses Paid (Recovered) on Financial Guaranty Insurance Contracts
Subtotal	800,000	700,000	16,500,000	3,000,000
Total	800,000	700,000	16,500,000	3,000,000
CES | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	22,600,000	4,800,000	7,000,000	(2,300,000)
Net Losses Paid (Recovered) on Financial Guaranty Insurance Contracts
Subtotal	1,500,000	20,100,000	43,200,000	60,000,000
Total	1,500,000	20,100,000	43,200,000	60,000,000
HELOCs | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	18,500,000	17,200,000	115,700,000	52,000,000
Net Losses Paid (Recovered) on Financial Guaranty Insurance Contracts
Subtotal	23,900,000	129,500,000	(638,800,000)	445,300,000
Total	23,900,000	129,500,000	(638,800,000)	445,300,000
Second lien | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	41,100,000	22,000,000	122,700,000	49,700,000
Net Losses Paid (Recovered) on Financial Guaranty Insurance Contracts
Subtotal	25,400,000	149,600,000	(595,600,000)	505,300,000
Total	25,400,000	149,600,000	(595,600,000)	505,300,000
Other Structured finance. | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	83,800,000	15,000,000	115,200,000	51,600,000
Net Losses Paid (Recovered) on Financial Guaranty Insurance Contracts
Subtotal	4,700,000	1,900,000	7,700,000	7,500,000
Total	4,700,000	1,900,000	7,700,000	7,500,000
Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	252,600,000	120,900,000	418,600,000	351,600,000
Net Losses Paid (Recovered) on Financial Guaranty Insurance Contracts
Subtotal	152,200,000	243,500,000	(233,900,000)	719,400,000
Total	152,200,000	243,500,000	(233,900,000)	719,400,000
Other
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	200,000	100,000	200,000	200,000
Net Losses Paid (Recovered) on Financial Guaranty Insurance Contracts
Subtotal		$ 200,000		$ 200,000