Financial Guaranty Insurance Contracts (Details 12) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2011 Y Contracts	Dec. 31, 2010 Y Contracts	Jun. 30, 2010	Dec. 31, 2009
Reserves (salvage)
Total BIG, Net	$ 92,100,000	$ (393,600,000)
Effect of consolidating FG VIEs	(128,100,000)	(42,700,000)
Total	220,200,000	(350,900,000)
BIG 1 | Financial Guaranty
Number of risks
Gross	151	119
Ceded	(60)	(45)
Remaining weighted average contract period
Gross (in years)	11.5	11.7
Ceded (in years)	14.8	16.0
Principal
Gross	7,724,400,000	6,173,000,000
Ceded	(847,400,000)	(723,300,000)
Interest
Gross	4,074,500,000	3,599,500,000
Ceded	(655,800,000)	(580,400,000)
Total net outstanding exposure
Gross	11,798,900,000	9,772,500,000
Ceded	(1,503,200,000)	(1,303,700,000)
Expected cash flows
Gross	228,500,000	303,900,000
Ceded	(8,400,000)	(20,200,000)
Less: Potential recoveries
Gross	(378,200,000)	(375,200,000)
Ceded	26,900,000	37,400,000
Subtotal
Gross	(149,700,000)	(71,300,000)
Ceded	18,500,000	17,200,000
Discount
Gross	42,300,000	(21,000,000)
Ceded	(1,100,000)	(5,500,000)
Present value of expected cash flows
Gross	(107,400,000)	(92,300,000)
Ceded	17,400,000	11,700,000
Deferred premium revenue
Gross	141,800,000	169,900,000
Ceded	(14,400,000)	(16,900,000)
Reserves (salvage)
Gross	(115,900,000)	(112,900,000)
Ceded	17,900,000	12,400,000
BIG 2 | Financial Guaranty
Number of risks
Gross	84	98
Ceded	(29)	(42)
Remaining weighted average contract period
Gross (in years)	9.3	8.4
Ceded (in years)	7.1	7.9
Principal
Gross	5,245,600,000	5,899,300,000
Ceded	(207,500,000)	(182,800,000)
Interest
Gross	2,566,700,000	2,601,600,000
Ceded	(70,400,000)	(70,900,000)
Total net outstanding exposure
Gross	7,812,300,000	8,500,900,000
Ceded	(277,900,000)	(253,700,000)
Expected cash flows
Gross	1,548,400,000	2,036,600,000
Ceded	(85,800,000)	(68,900,000)
Less: Potential recoveries
Gross	(633,700,000)	(533,000,000)
Ceded	23,400,000	16,600,000
Subtotal
Gross	914,700,000	1,503,600,000
Ceded	(62,400,000)	(52,300,000)
Discount
Gross	(441,900,000)	(613,200,000)
Ceded	38,300,000	(21,500,000)
Present value of expected cash flows
Gross	472,800,000	890,400,000
Ceded	(24,100,000)	(30,800,000)
Deferred premium revenue
Gross	357,700,000	572,400,000
Ceded	(23,400,000)	(30,300,000)
Reserves (salvage)
Gross	281,400,000	424,400,000
Ceded	(14,600,000)	(9,500,000)
BIG 3 | Financial Guaranty
Number of risks
Gross	129	115
Ceded	(51)	(42)
Remaining weighted average contract period
Gross (in years)	8.7	8.8
Ceded (in years)	6.0	6.0
Principal
Gross	8,102,600,000	7,954,500,000
Ceded	(678,400,000)	(673,600,000)
Interest
Gross	2,343,800,000	2,490,700,000
Ceded	(178,300,000)	(186,300,000)
Total net outstanding exposure
Gross	10,446,400,000	10,445,200,000
Ceded	(856,700,000)	(859,900,000)
Expected cash flows
Gross	2,715,300,000	2,256,600,000
Ceded	(144,300,000)	(133,200,000)
Less: Potential recoveries
Gross	(2,229,600,000)	(2,543,600,000)
Ceded	103,800,000	197,500,000
Subtotal
Gross	485,700,000	(287,000,000)
Ceded	(40,500,000)	64,300,000
Discount
Gross	(83,100,000)	(139,600,000)
Ceded	(7,800,000)	(7,900,000)
Present value of expected cash flows
Gross	402,600,000	(426,600,000)
Ceded	(48,300,000)	56,400,000
Deferred premium revenue
Gross	1,084,600,000	995,900,000
Ceded	(129,900,000)	(120,700,000)
Reserves (salvage)
Gross	(86,300,000)	815,900,000
Ceded	(7,500,000)	105,800,000
Financial Guaranty
Number of risks
Total BIG, Net	364	332
Total	364	332
Remaining weighted average contract period
Total BIG, Net (in years)	9.8	9.6
Total (in years)	9.8	9.6
Principal
Total BIG, Net	19,339,300,000	18,447,100,000
Total	19,339,300,000	18,447,100,000
Interest
Total BIG, Net	8,080,500,000	7,854,200,000
Total	8,080,500,000	7,854,200,000
Total net outstanding exposure
Total BIG, Net	27,419,800,000	26,301,300,000
Total	27,419,800,000	26,301,300,000
Expected cash flows
Total BIG, Net	4,253,700,000	4,374,800,000
Effect of Consolidating VIEs	(593,800,000)	(384,200,000)
Total	3,659,900,000	3,990,600,000
Less: Potential recoveries
Total BIG, Net	(3,087,400,000)	(3,200,300,000)
Effect of Consolidating VIEs	588,200,000	354,800,000
Total	(2,499,200,000)	(2,845,500,000)
Subtotal
Total BIG, NET	1,166,300,000	1,174,500,000
Effect of Consolidating VIEs	(5,600,000)	(29,400,000)
Total	1,160,700,000	1,145,100,000
Discount
Total BIG, Net	(453,300,000)	(765,700,000)
Effect of Consolidating VIEs	11,200,000	(19,800,000)
Total	(442,100,000)	(785,500,000)
Present value of expected cash flows
Total BIG, Net	713,000,000	408,800,000	766,900,000	1,066,400,000
Effect of Consolidating VIEs	5,600,000	(49,200,000)
Total	718,600,000	359,600,000
Deferred premium revenue
Total BIG, Net	1,416,400,000	1,570,300,000
Effect of Consolidating VIEs	(420,900,000)	(263,900,000)
Total	995,500,000	1,306,400,000
Reserves (salvage)
Total BIG, Net	90,000,000	(395,700,000)
Effect of consolidating FG VIEs	(128,100,000)	42,700,000
Total	$ 218,100,000	$ (353,000,000)