Financial Guaranty Insurance Contracts (Details 2) (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
Net Earned Premiums
Accretion of discount on net premiums receivable									$ 31,800,000	$ 43,100,000	$ 27,700,000
Net earned premiums	225,000,000	211,100,000	230,000,000	254,000,000	286,300,000	288,700,000	297,000,000	314,700,000	920,055,000	1,186,705,000	930,429,000
Net earned premium related to consolidated FG VIEs									74,700,000	47,600,000
Gross premium receivable, net of ceding commissions payable:
Balance beginning of period				1,167,587,000				1,418,200,000	1,167,587,000	1,418,200,000	15,700,000
Change in accounting										(19,000,000)	721,500,000
Balance beginning of the period, adjusted	1,167,600,000				1,399,200,000				1,167,600,000	1,399,200,000	737,200,000
Premiums receivable purchased in AGMH acquisition on July 1, 2009 after intercompany eliminations											800,900,000
Premium written, net									244,600,000	347,100,000	594,500,000
Premium payments received, net									(317,600,000)	(486,800,000)	(736,400,000)
Adjustments to the premium receivable:
Changes in the expected term of financial guaranty insurance contracts									(104,000,000)	(101,800,000)	(37,500,000)
Accretion of discount									31,800,000	43,100,000	27,700,000
Foreign exchange translation									(5,100,000)	(31,400,000)	37,000,000
Consolidation of FG VIEs									(9,800,000)	(6,500,000)
Other adjustments									(4,600,000)	(4,700,000)	(5,200,000)
Balance end of period	1,002,852,000				1,167,587,000				1,002,852,000	1,167,587,000	1,418,200,000
Premium written related to FG insurance which replaced existing credit derivative contracts									16,100,000
Gross premium receivable, net of ceding commissions of consolidated FG VIEs	27,500,000				23,400,000				27,500,000	23,400,000
Percentage of installment premium receivables denominated in currencies other than the U.S. dollar	47.00%				42.00%				47.00%	42.00%
Gross premium collections expected:
Cash collections on FG VIEs	33,300,000								33,300,000
Financial Guaranty
Net Earned Premiums
Scheduled net earned premiums									764,600,000	1,054,400,000	724,900,000
Acceleration of premium earnings									125,200,000	90,000,000	173,800,000
Accretion of discount on net premiums receivable									28,500,000	39,900,000	28,700,000
Total net earned premiums									918,300,000	1,184,300,000	927,400,000
Adjustments to the premium receivable:
Accretion of discount									28,500,000	39,900,000	28,700,000
Gross premium collections expected:
2012 (January 1 - March 31)	56,200,000								56,200,000
2012 (April 1 - June 30)	40,600,000								40,600,000
2012 (July 1 - September 30)	28,400,000								28,400,000
2012 (October 1 - December 31)	42,800,000								42,800,000
2013	104,300,000								104,300,000
2014	92,100,000								92,100,000
2015	81,800,000								81,800,000
2016	75,900,000								75,900,000
2017-2021	299,100,000								299,100,000
2022-2026	200,300,000								200,300,000
2027-2031	146,500,000								146,500,000
After 2031	178,600,000								178,600,000
Total	1,346,600,000								1,346,600,000
Other
Net Earned Premiums
Net earned premiums									$ 1,800,000	$ 2,400,000	$ 3,000,000