Expected Losses to be Paid (US RMBS Risks With R&W Benefit) (Details 7) (USD $)	3 Months Ended																																						3 Months Ended		3 Months Ended			1 Months Ended
	Mar. 31, 2013 risk		Mar. 31, 2012	Dec. 31, 2012 risk		Mar. 31, 2013 Prime first lien risk		Dec. 31, 2012 Prime first lien risk		Mar. 31, 2013 Alt-A first lien risk		Dec. 31, 2012 Alt-A first lien risk		Mar. 31, 2013 First mortgage, option adjustable rate mortgage risk		Dec. 31, 2012 First mortgage, option adjustable rate mortgage risk		Mar. 31, 2013 First mortgage, subprime risk		Dec. 31, 2012 First mortgage, subprime risk		Mar. 31, 2013 Closed end second lien and HELOCs risk		Dec. 31, 2012 Closed end second lien and HELOCs risk		Mar. 31, 2013 HELOCs risk		Dec. 31, 2012 HELOCs risk		Mar. 31, 2013 Second lien loan	Mar. 31, 2013 Total first lien loan	Mar. 31, 2013 Bank of America Agreement	Apr. 14, 2011 Bank of America Agreement	Mar. 31, 2013 Deutsche Bank Agreement	May 08, 2012 Deutsche Bank Agreement Transaction	Mar. 31, 2013 Deutsche Bank Agreement Covered Transactions	May 08, 2012 Deutsche Bank Agreement Covered Transactions Transaction	May 08, 2012 Deutsche Bank Agreement Uninsured tranches of covered transactions	Mar. 31, 2013 UBS	May 06, 2013 UBS	Mar. 31, 2013 Minimum	Mar. 31, 2013 Maximum	Mar. 31, 2013 Maximum Deutsche Bank Agreement Uninsured tranches of covered transactions	Feb. 28, 2013 Flagstar [Member]
Guarantor Obligations [Line Items]
Collateral Losses																																$ 3,300,000,000
Loss Sharing Percentage																																	80.00%							85.00%
Maximum Loss Up To Which Loss Sharing Percentage Applicable																																	6,600,000,000
Assets held under trust for reimbursement payment																																749,000,000
Number of Transactions Settled Through Litigation																																			3
Financial Guaranty Insurance Contracts Total Recoveries Under Negotiated Agreement	1,700,000,000
Number of Risks as of the end of the period with R&W Benefit Recorded (in policies)	55	[1]		53	[1]	1	[1]	1	[1]	28	[1]	26	[1]	10	[1]	10	[1]	5	[1]	5	[1]	4	[1]	4	[1]	7	[1]	7	[1]
Outstanding Principal and Interest on Representations and Warranties Policies	6,335,000,000			6,731,000,000		33,000,000		35,000,000		3,929,000,000		4,030,000,000		926,000,000		1,101,000,000		810,000,000		820,000,000		119,000,000		196,000,000		518,000,000		549,000,000
Eligible assets to be placed in trust to collateralize the obligations of a reinsurance affiliate																																		274,000,000
Number of transactions insured																																					8
Estimated Cumulative Collateral Losses																																5,100,000,000
Loss sharing percentage, first layer																																					80.00%
Maximum aggregate collateral losses up to which first layer of loss sharing will be applicatble																																					319,000,000	141,000,000
Minimum losses at which second later of loss sharing percentage becomes applicable																																					389,000,000	161,000,000
Loss sharing percentage, second layer																																					85.00%	60.00%
Maximum aggregate collateral losses up to which second layer of loss sharing will be applicable																																					600,000,000
Insured financial obligations gross outstanding principal amount																																3,300,000,000				516,000,000			276,700,000
Financial Guaranty Insurance Contracts Expected Future Recoveries for Breached Representations and Warranties Increase Due to Negotiated Agreements	142,000,000		48,000,000																																				142,000,000
Insured Financial Obligations Outstanding Principal Amount	501,817,000,000			519,893,000,000		619,000,000		641,000,000		4,439,000,000		4,589,000,000		1,387,000,000		1,550,000,000		7,130,000,000		7,330,000,000						3,059,000,000		3,196,000,000				3,100,000,000
Insured Financial Obligations Net Outstanding Principal Amount																																				444,000,000
Minimum losses at which third layer of loss sharing percentage becomes applicable																																						185,000,000
Loss sharing percentage, third layer																																						100.00%
Maximum aggregate collateral losses up to which third layer of loss sharing will be applicable																																						248,000,000
Losses Incurred by the Company																																											146,000,000
Estimated Benefit From Loan Repurchases Related to Breaches of R and W Included in Net Expected Loss Estimates Under Agreements Other	51,000,000
Judgment granted in favor of AGM																																												106,500,000
Estimated Benefit From Loan Repurchases Related to Breaches of R and W Included in Net Expected Loss Estimates	1,400,000,000
Estimated Benefit From Loan Repurchases Related to Breaches of R and W Included in Net Expected Loss Estimates Under Agreements	1,037,000,000
Estimated Benefit From Loan Repurchases Related to Breaches of R and W Included in Net Expected Loss Estimates in Pursuit	401,000,000
Number of defaulted loan files reviewed																														41,400	16,600
Outstanding par of defaulted loans reviewed																														3,100,000,000	6,000,000,000
Number of loan files that breached one or more R&W																														3,800	20,800
Amount of loans to be repurchased by providers																														276,000,000	6,300,000,000
Amount of Liabilities Agreed Paid by Entities Providing R and Ws for Transactions Company Provided a Financial Guaranty	3,400,000,000
Amount of Liabilities Agreed Paid Directly to the Company by Entities Providing R and Ws for Transactions the Company Provided a Financial Guaranty	2,800,000,000
Amount of Liabilities Agreed Paid Into Relevant RMBS Financial Guaranty Transactions Entities Providing R and Ws to the Company for Financial Guaranty Transactions	562,000,000
Cash amount already received for liabilities agreed paid by entities providing R and Ws for transactions the Company provided a financial guaranty	2,100,000,000																																							358,000,000
Cash Expected to be Received From Liabilities Agreed Paid by Entities Providing R and Ws for Transactions the Company Provided a Financial Guaranty	$ 716,000,000
Estimated Period of Recoveries on Transactions Backed by HELOC and Closed End Second Lien Loans Not Subject to settlement Agreements																																									2 years	4 years

[1] A risk represents the aggregate of the financial guaranty policies that share the same revenue source for purposes of making Debt Service payments.