Financial Guaranty Insurance Contracts (Details 10)			3 Months Ended		1 Months Ended	3 Months Ended										3 Months Ended	12 Months Ended				3 Months Ended						3 Months Ended
	Mar. 31, 2012 USD ($) Transaction	Dec. 31, 2011 USD ($)	Mar. 31, 2012 "XXX" Life Insurance Transactions Below investment grade ("BIG") USD ($)	Mar. 31, 2012 Student Loan USD ($)	Jun. 30, 2011 Trust preferred securities collateralized debt obligations Transaction	Mar. 31, 2012 Trust preferred securities collateralized debt obligations USD ($) Transaction	Mar. 31, 2012 Trust preferred securities collateralized debt obligations Below investment grade ("BIG") USD ($)	Mar. 31, 2012 Public finance student loan USD ($)	Mar. 31, 2012 Public finance student loan Below investment grade ("BIG") USD ($)	Mar. 31, 2012 Asset-backed student loan USD ($)	Mar. 31, 2012 Asset-backed student loan Below investment grade ("BIG") USD ($)	Mar. 31, 2012 Jefferson County Alabama Sewer Authority USD ($)	Dec. 31, 2011 Jefferson County Alabama Sewer Authority USD ($)	Mar. 31, 2012 Telephone directory "yellow pages" USD ($)	Dec. 31, 2011 Telephone directory "yellow pages" USD ($)	Mar. 31, 2012 Manufactured housing loans USD ($) Transaction	Dec. 31, 2011 Manufactured housing loans USD ($) Transaction	Mar. 31, 2012 Manufactured housing loans Below investment grade ("BIG") USD ($)	Mar. 31, 2012 Harrisburg, Pennsylvania USD ($)	Mar. 31, 2012 Harrisburg, Pennsylvania Below investment grade ("BIG") USD ($)	Mar. 31, 2012 Sovereign debt of Greece with a 4.5% fixed coupon USD ($)	Mar. 31, 2012 Sovereign debt of Greece with a 4.5% fixed coupon EUR (€)	Dec. 31, 2011 Sovereign debt of Greece with a 4.5% fixed coupon USD ($)	Mar. 31, 2012 Total first lien Transaction	Mar. 31, 2012 Jefferson County Alabama Sewer Authority Warrants USD ($)	Mar. 31, 2012 Jefferson County Alabama Sewer Authority Bonds USD ($)	Mar. 31, 2012 Sovereign debt of Greece due in 2057 with a 2.085% inflation-linked coupon EUR (€)
Financial guarantee obligations
Net exposure of debt												$ 710,400,000										€ 165,100,000					€ 52,600,000
Exposure of debt																						200,000,000					114,100,000
Coupon rate (as a percent)																					4.50%	4.50%					2.085%
Weighted-average discounted loss posted by the Company, gross of reinsurance																					334,100,000		64,700,000
Weighted average discounted loss posted by the Company, net of reinsurance																					231,900,000		42,600,000
Net Par Outstanding Financial Guaranty Insurance			2,300,000,000	2,800,000,000		1,800,000,000	796,700,000	1,500,000,000	609,600,000	1,300,000,000	170,700,000	478,500,000		110,000,000		326,900,000		221,300,000	168,800,000	94,800,000					273,100,000	205,400,000
Gross expected loss	954,475,000	679,011,000	882,500,000	9,200,000								50,400,000	26,700,000		21,900,000
Largest expected loss to be paid for a single transaction				24,700,000		8,500,000																				23,700,000
Projected net expected loss			122,700,000	65,400,000								231,800,000
Number of TruPS CDOs for which the company is projecting losses						0
Number of TruPS CDOs converted to financial guaranty form					0
Number of direct transactions for which estimated loss was projected																	2
Expected loss on direct transactions																16,600,000	18,400,000								168,100,000	63,700,000
Net par of contracts for which estimated loss was projected																140,900,000
Expected loss on assumed transactions																									100,000
Number of assumed transactions for which estimated loss was projected																1
Net par of assumed contracts for which estimated loss was projected																4,900,000
Net claims to date																			8,000,000
Number of U.S. RMBS transactions for which lawsuits were filed alleging breaches of R&W																								6
Number of U.S. RMBS transactions for which lawsuits were filed alleging violations of state securities laws and other claims	2
Decrease in projected expected loss to be paid			$ 6,800,000			$ 4,700,000
Number of U.S. RMBS transactions for which a complaint was filed against UBS Real Estate	3