Financial Guaranty Insurance Contracts (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Net Earned Premiums
Accretion of discount on net premiums receivable			$ 22,800,000	$ 35,100,000
Net earned premiums	211,073,000	288,767,000	695,118,000	900,437,000
Net earned premium related to consolidated FG VIEs	19,400,000	12,800,000	56,800,000	34,400,000
Gross premium receivable, net of ceding commissions payable:
Balance beginning of period	1,167,600,000	1,418,200,000	1,167,600,000	1,418,200,000
Change in accounting				(19,000,000)
Balance beginning of the period, adjusted			1,167,587,000	1,399,200,000
Premium written, net			153,200,000	253,900,000
Premium payments received, net			(227,800,000)	(356,300,000)
Adjustments to the premium receivable:
Changes in the expected term of financial guaranty insurance contracts			(117,100,000)	13,200,000
Accretion of discount			22,800,000	35,100,000
Foreign exchange translation			(3,100,000)	(24,200,000)
Other adjustments			(8,500,000)	1,600,000
Balance, end of period	987,115,000	1,322,500,000	987,115,000	1,322,500,000
Percentage of installment premium receivables denominated in currencies other than the U.S. dollar (as a percent)	49.00%		49.00%		42.00%
Premium written related to FG insurance which replaced existing credit derivative contracts			14,900,000
Financial Guaranty
Net Earned Premiums
Scheduled net earned premiums	178,100,000	256,400,000	595,700,000	814,700,000
Acceleration of premium earnings	26,800,000	21,200,000	77,400,000	52,000,000
Accretion of discount on net premiums receivable	5,800,000	10,500,000	20,600,000	31,800,000
Total net earned premiums	210,700,000	288,100,000	693,700,000	898,500,000
Adjustments to the premium receivable:
Accretion of discount	5,800,000	10,500,000	20,600,000	31,800,000
Gross premium collections expected:
2011 (October 1 - December 31)	75,500,000		75,500,000
2012	119,000,000		119,000,000
2013	101,300,000		101,300,000
2014	89,200,000		89,200,000
2015	78,800,000		78,800,000
2016-2020	306,800,000		306,800,000
2021-2025	212,200,000		212,200,000
2026-2030	154,200,000		154,200,000
After 2030	204,700,000		204,700,000
Total gross expected collections	1,341,700,000		1,341,700,000
Total gross expected collections related to VIEs	35,000,000		35,000,000
Total	1,376,700,000		1,376,700,000
Other
Net Earned Premiums
Net earned premiums	$ 400,000	$ 600,000	$ 1,400,000	$ 1,900,000