Financial Guaranty Contracts Accounted for as Insurance (Details 11) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	$ 152,500,000	$ 95,500,000	$ 177,400,000	$ 236,000,000
Effect of consolidating FG VIEs	(19,600,000)	(24,300,000)	(71,500,000)	(34,300,000)
Total loss and LAE	132,908,000	71,156,000	105,861,000	201,657,000	413,800,000	377,800,000	265,800,000
Net Losses Paid on Financial Guaranty Insurance Contracts
Subtotal	(610,700,000)	247,000,000	(386,100,000)	475,900,000
Effect of consolidating FG VIEs	46,000,000	(41,000,000)	(12,200,000)	(58,900,000)
Total	(564,700,000)	206,000,000	(398,300,000)	417,000,000
Public finance | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	4,100,000	(16,800,000)	(11,700,000)	10,900,000
Net Losses Paid on Financial Guaranty Insurance Contracts
Subtotal	200,000	9,800,000	9,200,000	34,200,000
Total			9,200,000	34,200,000
Total first lien | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	95,100,000	80,900,000	64,700,000	155,500,000
Net Losses Paid on Financial Guaranty Insurance Contracts
Subtotal	101,200,000	49,100,000	222,700,000	80,400,000
Total			222,700,000	80,400,000
U.S. RMBS | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	125,600,000	80,600,000	146,300,000	183,200,000
Net Losses Paid on Financial Guaranty Insurance Contracts
Subtotal	(611,500,000)	235,300,000	(398,300,000)	436,100,000
Total			(398,300,000)	436,100,000
Prime first lien | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	1,200,000	(100,000)	1,100,000
Alt-A first lien | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	19,200,000	8,100,000	27,400,000	13,500,000
Net Losses Paid on Financial Guaranty Insurance Contracts
Subtotal	19,100,000	15,000,000	38,600,000	29,000,000
Total			38,600,000	29,000,000
Option ARM | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	70,400,000	56,600,000	41,300,000	101,000,000
Net Losses Paid on Financial Guaranty Insurance Contracts
Subtotal	81,500,000	32,700,000	168,400,000	49,100,000
Total			168,400,000	49,100,000
Subprime | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	4,300,000	16,300,000	(5,100,000)	41,000,000
Net Losses Paid on Financial Guaranty Insurance Contracts
Subtotal	600,000	1,400,000	15,700,000	2,300,000
Total			15,700,000	2,300,000
CES | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	(5,700,000)	(11,500,000)	(15,600,000)	(7,100,000)
Net Losses Paid on Financial Guaranty Insurance Contracts
Subtotal	14,600,000	19,400,000	41,700,000	39,900,000
Total			41,700,000	39,900,000
HELOCs | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	36,200,000	11,200,000	97,200,000	34,800,000
Net Losses Paid on Financial Guaranty Insurance Contracts
Subtotal	(727,300,000)	166,800,000	(662,700,000)	315,800,000
Total			(662,700,000)	315,800,000
Second lien | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	30,500,000	(300,000)	81,600,000	27,700,000
Net Losses Paid on Financial Guaranty Insurance Contracts
Subtotal	(712,700,000)	186,200,000	(621,000,000)	355,700,000
Total			(621,000,000)	355,700,000
Other Structured finance. | Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	22,800,000	31,600,000	42,800,000	41,800,000
Net Losses Paid on Financial Guaranty Insurance Contracts
Subtotal	600,000	1,900,000	3,000,000	5,600,000
Total			3,000,000	5,600,000
Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	152,500,000	95,400,000	177,400,000	235,900,000
Net Losses Paid on Financial Guaranty Insurance Contracts
Subtotal	(610,700,000)	247,000,000	(386,100,000)	475,900,000
Total			(386,100,000)	475,900,000
Other
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal		$ 100,000		$ 100,000