Financial Guaranty Insurance Contracts (Details 4) (USD $)						6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	3 Months Ended				6 Months Ended					3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended					12 Months Ended	3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011		Dec. 31, 2010	Jun. 30, 2012 U.S. dollar denominated obligations Minimum	Dec. 31, 2011 U.S. dollar denominated obligations Minimum	Jun. 30, 2012 U.S. dollar denominated obligations Maximum	Dec. 31, 2011 U.S. dollar denominated obligations Maximum	Jun. 30, 2012 Financial Guaranty		Jun. 30, 2011 Financial Guaranty		Jun. 30, 2012 Financial Guaranty		Jun. 30, 2011 Financial Guaranty		Dec. 31, 2011 Financial Guaranty	Jun. 30, 2012 Financial Guaranty U.S. RMBS		Jun. 30, 2011 Financial Guaranty U.S. RMBS		Jun. 30, 2012 Financial Guaranty U.S. RMBS		Jun. 30, 2011 Financial Guaranty U.S. RMBS		Jun. 30, 2012 Financial Guaranty Total first lien		Jun. 30, 2011 Financial Guaranty Total first lien		Jun. 30, 2012 Financial Guaranty Total first lien		Jun. 30, 2011 Financial Guaranty Total first lien		Jun. 30, 2012 Financial Guaranty Prime first lien		Jun. 30, 2011 Financial Guaranty Prime first lien		Jun. 30, 2012 Financial Guaranty Prime first lien		Jun. 30, 2011 Financial Guaranty Prime first lien		Jun. 30, 2012 Financial Guaranty Alt-A first lien		Jun. 30, 2011 Financial Guaranty Alt-A first lien		Jun. 30, 2012 Financial Guaranty Alt-A first lien		Jun. 30, 2011 Financial Guaranty Alt-A first lien		Jun. 30, 2012 Financial Guaranty Option ARM		Jun. 30, 2011 Financial Guaranty Option ARM		Jun. 30, 2012 Financial Guaranty Option ARM		Jun. 30, 2011 Financial Guaranty Option ARM		Jun. 30, 2012 Financial Guaranty Subprime		Jun. 30, 2011 Financial Guaranty Subprime		Jun. 30, 2012 Financial Guaranty Subprime		Jun. 30, 2011 Financial Guaranty Subprime		Jun. 30, 2012 Financial Guaranty Second lien		Jun. 30, 2011 Financial Guaranty Second lien		Jun. 30, 2012 Financial Guaranty Second lien		Jun. 30, 2011 Financial Guaranty Second lien		Jun. 30, 2012 Financial Guaranty CES		Jun. 30, 2011 Financial Guaranty CES		Jun. 30, 2012 Financial Guaranty CES		Jun. 30, 2011 Financial Guaranty CES		Jun. 30, 2012 Financial Guaranty HELOCs		Jun. 30, 2011 Financial Guaranty HELOCs		Jun. 30, 2012 Financial Guaranty HELOCs		Jun. 30, 2011 Financial Guaranty HELOCs		Jun. 30, 2012 Financial Guaranty TruPS [Member]		Jun. 30, 2011 Financial Guaranty TruPS [Member]		Jun. 30, 2012 Financial Guaranty TruPS [Member]		Jun. 30, 2011 Financial Guaranty TruPS [Member]		Jun. 30, 2012 Financial Guaranty Structured finance		Jun. 30, 2011 Financial Guaranty Structured finance		Jun. 30, 2012 Financial Guaranty Structured finance		Jun. 30, 2011 Financial Guaranty Structured finance		Jun. 30, 2012 Financial Guaranty US Public Finance [Member]		Jun. 30, 2011 Financial Guaranty US Public Finance [Member]		Jun. 30, 2012 Financial Guaranty US Public Finance [Member]		Jun. 30, 2011 Financial Guaranty US Public Finance [Member]		Jun. 30, 2012 Financial Guaranty Public finance Non-U.S.		Jun. 30, 2011 Financial Guaranty Public finance Non-U.S.		Jun. 30, 2012 Financial Guaranty Public finance Non-U.S.		Jun. 30, 2011 Financial Guaranty Public finance Non-U.S.		Jun. 30, 2012 Policies Paid in Installments	Dec. 31, 2011 Policies Paid in Installments	Jun. 30, 2012 Other		Jun. 30, 2011 Other		Jun. 30, 2012 Other		Jun. 30, 2011 Other		Jun. 30, 2012 Financial Guaranty and Other [Member]		Jun. 30, 2011 Financial Guaranty and Other [Member]		Jun. 30, 2012 Financial Guaranty and Other [Member]		Jun. 30, 2011 Financial Guaranty and Other [Member]
Financial guarantee obligations
Fair Value Inputs, Discount Rate						0.00%	0.00%	3.04%	3.27%
Selected Information for Policies Paid in Installments
Premiums receivable, net of ceding commissions payable	$ 964,063,000	$ 1,002,852,000	$ 1,059,500,000	[1]	$ 1,167,600,000																																																																																																																						$ 964,100,000	$ 1,002,900,000
Gross deferred premium revenue										5,698,600,000				5,698,600,000				6,046,300,000																																																																																																									2,013,100,000	2,192,600,000
Weighted-average risk-free rate used to discount premiums (as a percent)																																																																																																																											3.60%	3.40%
Weighted-average period of premiums receivable (in years)																																																																																																																											10 years	9 years 9 months 18 days
Present Value of Net Expected Loss to be paid Roll Forward by Sector
Net Expected Loss to be Paid, at the beginning of the period	826,500,000									752,400,000		32,200,000		638,000,000	[2]	408,800,000			212,600,000		(207,100,000)		319,200,000	[2]	160,800,000		344,800,000		662,500,000		429,900,000	[2]	909,900,000		2,200,000		1,500,000		1,800,000	[2]	1,400,000		116,900,000		171,400,000		134,900,000	[2]	184,400,000		75,300,000		322,100,000		152,900,000	[2]	523,700,000		150,400,000		167,500,000		140,300,000	[2]	200,400,000		(132,200,000)		(869,600,000)		(110,700,000)	[2]	(749,100,000)		(89,700,000)		(76,900,000)		(79,600,000)	[2]	56,600,000		(42,500,000)		(792,700,000)		(31,100,000)	[2]	(805,700,000)		8,500,000		(900,000)		13,200,000	[2]	(600,000)		196,800,000		173,900,000		239,600,000	[2]	159,700,000		32,700,000		55,900,000		15,800,000	[2]	81,600,000		301,800,000		10,400,000		50,200,000	[2]	7,300,000				1,900,000		2,100,000		1,900,000	[2]	2,100,000		754,300,000		34,300,000		639,900,000	[2]	410,900,000
Economic Loss Development										96,600,000	[3]	70,100,000	[3]	301,400,000	[3]	(81,900,000)	[3]		47,000,000	[3]	61,800,000	[3]	54,900,000	[3]	(92,900,000)	[3]	34,800,000	[3]	37,900,000	[3]	36,200,000	[3]	(88,000,000)	[3]	700,000	[3]	1,700,000	[3]	1,100,000	[3]	1,800,000	[3]	22,800,000	[3]	15,300,000	[3]	14,200,000	[3]	21,800,000	[3]	700,000	[3]	26,300,000	[3]	(1,000,000)	[3]	(88,400,000)	[3]	10,600,000	[3]	(5,400,000)	[3]	21,900,000	[3]	(23,200,000)	[3]	12,200,000	[3]	23,900,000	[3]	18,700,000	[3]	(4,900,000)	[3]	(2,600,000)	[3]	(3,200,000)	[3]	(3,700,000)	[3]	(109,600,000)	[3]	14,800,000	[3]	27,100,000	[3]	22,400,000	[3]	104,700,000	[3]	(1,800,000)	[3]	7,000,000	[3]	(6,300,000)	[3]	7,000,000	[3]	30,900,000	[3]	1,200,000	[3]	11,600,000	[3]	17,500,000	[3]	35,500,000	[3]	3,700,000	[3]	58,300,000	[3]	(13,000,000)	[3]	(15,000,000)	[3]	(3,600,000)	[3]	182,900,000	[3]	(500,000)	[3]			(6,000,000)	[3]	0	[3]	(6,000,000)	[3]	0	[3]	90,600,000	[3]	70,100,000	[3]	295,400,000	[3]	(81,900,000)	[3]
(Paid) Recovered Losses										(22,500,000)	[4]	610,700,000	[4]	(112,900,000)	[4]	386,100,000	[4]		(21,600,000)	[4]	611,500,000	[4]	(136,100,000)	[4]	398,300,000	[4]	(61,500,000)	[4]	(101,200,000)	[4]	(148,000,000)	[4]	(222,700,000)	[4]	0	[4]	0	[4]	0	[4]	0	[4]	52,400,000	[4]	(19,100,000)	[4]	43,000,000	[4]	(38,600,000)	[4]	(112,300,000)	[4]	(81,500,000)	[4]	(188,200,000)	[4]	(168,400,000)	[4]	(1,600,000)	[4]	(600,000)	[4]	(2,800,000)	[4]	(15,700,000)	[4]	39,900,000	[4]	712,700,000	[4]	11,900,000	[4]	621,000,000	[4]	75,900,000	[4]	(14,600,000)	[4]	66,900,000	[4]	(41,700,000)	[4]	(36,000,000)	[4]	727,300,000	[4]	(55,000,000)	[4]	662,700,000	[4]	(200,000)	[4]	(1,400,000)	[4]	(400,000)	[4]	(1,700,000)	[4]	(6,600,000)	[4]	800,000	[4]	(30,100,000)	[4]	(1,300,000)	[4]	(9,800,000)	[4]	(200,000)	[4]	(15,700,000)	[4]	(9,200,000)	[4]	15,700,000	[4]	0	[4]	69,400,000	[4]	0	[4]			0	[4]	0	[4]	0	[4]	0	[4]	(22,500,000)	[4]	610,700,000	[4]	(112,900,000)	[4]	386,100,000	[4]
Net Expected Loss to be Paid, at the end of the period	826,500,000									826,500,000	[2]	713,000,000		826,500,000	[2]	713,000,000			238,000,000	[2]	466,200,000		238,000,000	[2]	466,200,000		318,100,000	[2]	599,200,000		318,100,000	[2]	599,200,000		2,900,000	[2]	3,200,000		2,900,000	[2]	3,200,000		192,100,000	[2]	167,600,000		192,100,000	[2]	167,600,000		(36,300,000)	[2]	266,900,000		(36,300,000)	[2]	266,900,000		159,400,000	[2]	161,500,000		159,400,000	[2]	161,500,000		(80,100,000)	[2]	(133,000,000)		(80,100,000)	[2]	(133,000,000)		(16,400,000)	[2]	(94,700,000)		(16,400,000)	[2]	(94,700,000)		(63,700,000)	[2]	(38,300,000)		(63,700,000)	[2]	(38,300,000)		6,500,000	[2]	4,700,000		6,500,000	[2]	4,700,000		221,100,000	[2]	175,900,000		221,100,000	[2]	175,900,000		58,400,000	[2]	59,400,000		58,400,000	[2]	59,400,000		302,500,000	[2]	6,800,000		302,500,000	[2]	6,800,000				(4,100,000)	[2]	2,100,000		(4,100,000)	[2]	2,100,000		822,400,000	[2]	715,100,000		822,400,000	[2]	715,100,000
Period after the end of the reporting period within which the ceded paid losses are typically settled (in days)	45 days
Expected LAE for mitigating claim liabilities	$ 31,100,000	$ 35,500,000

[1] Excludes $31.7 million and $31.7 million as of June 30, 2012 and 2011, respectively, related to consolidated FG VIEs.

[2] Includes expected LAE to be paid for mitigating claim liabilities of $31.1 million as of June 30, 2012 and $35.5 million as of December 31, 2011.

[3] Economic loss development includes the effects of changes in assumptions based on observed market trends, changes in discount rates, accretion of discount and the economic effects of loss mitigation efforts.

[4] Net of ceded paid losses, whether or not such amounts have been settled with reinsurers. Ceded paid losses are typically settled 45 days after the end of the reporting period. Such amounts are recorded in reinsurance recoverable on paid losses included in other assets.