Financial Guaranty Insurance Contracts (Details 10)	1 Months Ended	3 Months Ended		0 Months Ended	3 Months Ended			3 Months Ended													3 Months Ended				3 Months Ended
	Feb. 29, 2012 Transaction	Jun. 30, 2012 USD ($)	Dec. 31, 2011 USD ($)	May 25, 2012 ResCap and Debtors Adversary Proceeding in Us Bankruptcy Court in Souther District of New York [Member] Lawsuit defendants	Jun. 30, 2012 Life Insurance [Member] Below investment grade ("BIG") USD ($)	Jun. 30, 2012 Life Insurance [Member] Below investment grade ("BIG") Ballantyne Re Plc and Orkney Re II Plc [Member] Transaction	Jun. 30, 2012 Student Loan [Member] USD ($)	Jun. 30, 2012 Trust Preferred Securities Collateralized Debt Obligations [Member] USD ($)	Jun. 30, 2012 Trust Preferred Securities Collateralized Debt Obligations [Member] Below investment grade ("BIG") USD ($)	Jun. 30, 2012 Public Finance Student Loan [Member] USD ($)	Jun. 30, 2012 Public Finance Student Loan [Member] Below investment grade ("BIG") USD ($)	Jun. 30, 2012 Asset-backed Student Loan [Member] USD ($)	Jun. 30, 2012 Asset-backed Student Loan [Member] Below investment grade ("BIG") USD ($)	Jun. 30, 2012 Public Finance Jefferson County Alabama Sewer Authority [Member] USD ($)	Jun. 30, 2012 Public Finance City of Stockton Pension Obligation and Lease Revenue Bonds [Member] [Member] USD ($)	Jun. 30, 2012 Manufactured Housing Loans [Member] USD ($) Transaction	Dec. 31, 2011 Manufactured Housing Loans [Member] USD ($) Transaction	Jun. 30, 2012 Manufactured Housing Loans [Member] Below investment grade ("BIG") USD ($)	Jun. 30, 2012 Public Finance Harrisburg Pennsylvania [Member] USD ($)	Jun. 30, 2012 Public Finance Harrisburg Pennsylvania [Member] Below investment grade ("BIG") USD ($)	Jun. 30, 2012 Sovereign Debt [Member] USD ($)	Jun. 30, 2012 Sovereign Debt [Member] EUR (€)	Jun. 30, 2012 Public Finance Jefferson County Alabama Sewer Authority Bonds [Member] USD ($)	Jun. 30, 2012 Public Finance Jefferson County Alabama Sewer Authority Warrants [Member] USD ($)	Jun. 30, 2012 Sovereign Debt with Inflation Linked Rate [Member] EUR (€)	Jun. 30, 2012 Troubled Municipal Credits [Member] USD ($)	Mar. 31, 2012 Troubled Municipal Credits [Member] USD ($)
Financial guarantee obligations
Net Exposure of Debt														$ 708,700,000	$ 161,400,000							€ 165,100,000			€ 52,700,000
Claims Paid, Net															400,000
Exposure of Debt																						200,000,000			114,300,000
Coupon Rate (as a percent)																					4.50%				2.085%
Weighted-Average Discounted Loss posted by the Company, Gross of Reinsurance																					311,700,000
Weighted-Average Discounted Loss posted by the Company, Net of Reinsurance																					216,200,000
Foreign Currency Transaction Gain (Loss), before Tax																					15,600,000
Net Par Outstanding Financial Guaranty Insurance					2,300,000,000		2,700,000,000	1,700,000,000	745,100,000	1,300,000,000	447,400,000	1,400,000,000	170,100,000	478,500,000		316,200,000		214,900,000					205,400,000	273,100,000
Guaranty Liabilities																								31,900,000
Gross Expected Loss		995,217,000	679,011,000		882,500,000		2,700,000												155,200,000	94,900,000
Number of transactions insured						2
Largest Expected Loss to be Paid for a Single Transaction							27,400,000	6,500,000								21,400,000	18,400,000
Number of Direct Transactions With Expected Losses to be Paid																2	2
Commutation Payment Received From Ambac		7,000,000
Financial Guaranty Insurance Contracts Principal Amount Projected Estimated Loss																137,100,000
Number of Assumed Transactions With Expected Losses to be Paid																1	1
Financial Guaranty Insurance Assumed Contracts Principal Amount Projected Estimated Loss																4,800,000
Projected Net Expected Loss					135,300,000		62,700,000							198,300,000												58,400,000	32,700,000
Increase (Decrease) in Projected Expected Loss to be Paid					12,600,000			2,000,000
Net Claims to Date																			$ 8,600,000
Loss Contingency, Number of Defendants				42
Number of non-class action lawsuits filed				27
Number of First Lien Us Rmbs Transactions Agm Filed Complaint in Supreme Court of State of New York Against Ubs Real Estate Securities	3