Financial Guaranty Insurance Contracts (Details 2) (USD $)	9 Months Ended
	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2011 Financial Guaranty	Dec. 31, 2010 Financial Guaranty	Sep. 30, 2010 Financial Guaranty	Sep. 30, 2011 Other	Dec. 31, 2010 Other
Gross
Deferred premium revenue			$ 6,202,200,000	$ 7,108,600,000
Contra-paid			(99,400,000)	(146,100,000)
Total	6,111,822,000	6,972,894,000	6,102,800,000	6,962,500,000		9,000,000	10,400,000
Ceded
Deferred premium revenue			764,500,000	846,600,000
Contra-paid			(17,300,000)	(24,800,000)
Total	747,457,000	821,819,000	747,200,000	821,800,000		300,000
Net
Deferred premium revenue			5,437,700,000	6,262,000,000
Contra-paid			(82,100,000)	(121,300,000)	(183,500,000)
Total	5,364,300,000	6,151,100,000	5,355,600,000	6,140,700,000		8,700,000	10,400,000
Net unearned premium reserve related to FG VIE	311,500,000	193,200,000
Scheduled Net Earned Premium
2011 (October 1 - December 31)			167,200,000
2012			579,800,000
2013			483,000,000
2014			425,400,000
2015			376,000,000
2016 - 2020			1,406,100,000
2021 - 2025			882,400,000
2026 - 2030			538,300,000
After 2030			579,500,000
Total present value basis			5,437,700,000
Discount			308,900,000
Total future value			5,746,600,000
Net Expected Loss to be Expensed
2011 (October 1 - December 31)			40,700,000
2012			108,500,000
2013			65,700,000
2014			49,500,000
2015			38,000,000
2016 - 2020			144,700,000
2021 - 2025			70,200,000
2026 - 2030			39,200,000
After 2030			27,000,000
Total present value basis			583,500,000		1,073,000,000
Discount			353,800,000
Total future value			937,300,000
Net
2011 (October 1 - December 31)			126,500,000
2012			471,300,000
2013			417,300,000
2014			375,900,000
2015			338,000,000
2016 - 2020			1,261,400,000
2021 - 2025			812,200,000
2026 - 2030			499,100,000
After 2030			552,500,000
Total present value basis			4,854,200,000
Discount			(44,900,000)
Total future value			4,809,300,000
Reduction in future scheduled amortization of deferred premium revenue due to consolidating FG VIEs	(423,700,000)
Reduction in net present value of expected loss due to consolidating FG VIEs	$ (240,000,000)