Financial Guaranty Insurance Contracts (Details 9) (USD $)	3 Months Ended			6 Months Ended
	Jun. 30, 2012 Counterparty risk		Jun. 30, 2011	Jun. 30, 2012 risk		Jun. 30, 2011		Dec. 31, 2011 risk
Financial guarantee obligations
Number of Counterparties With Adjusted Projected Recovery That Resulted in the R and W Development	1
Estimated Benefit From Loan Repurchases Related to Breaches of R and W Included in Net Expected Loss Estimates	$ 1,200,000,000			$ 1,200,000,000
Amount of Liabilities Agreed Paid by Entities Providing R and Ws for Transactions Company Provided a Financial Guaranty	2,600,000,000
Amount of Liabilities Agreed Paid Directly to the Company by Entities Providing R and Ws for Transactions the Company Provided a Financial Guaranty	2,000,000,000
Cash Amount Already Received for Liabilities Agreed Paid by Entities Providing R and Ws for Transactions Company Provided a Financial Guaranty	1,473,000,000
Cash Expected to be Received From Liabilities Agreed Paid by Entities Providing R and Ws for Transactions the Company Provided a Financial Guaranty	568,000,000			568,000,000
Amount of Liabilities Agreed Paid Into Relevant RMBS Financial Guaranty Transactions Entities Providing R and Ws to the Company for Financial Guaranty Transactions	602,000,000
Salvage and subrogation recoverable
For all Financial Guaranty Insurance Contracts	313,100,000			313,100,000				401,800,000
Effect of Consolidating FG VIEs	(124,500,000)			(124,500,000)				(197,300,000)
Reported on Balance Sheet	188,600,000	[1]		188,600,000	[1]			204,500,000	[1]
Loss and LAE reserve
For all Financial Guaranty Insurance Contracts	740,700,000			740,700,000				857,500,000
Effect of Consolidating FG VIEs	(39,800,000)			(39,800,000)				(74,600,000)
Reported on Balance Sheet	700,900,000	[1]		700,900,000	[1]			782,900,000	[1]
Total
Benefit for R&W	1,212,900,000		1,473,300,000	1,212,900,000		1,473,300,000
Rollforward of Estimated Benefit from Recoveries of Representation and Warranty Breaches, Net of Reinsurance
Future Net R&W Benefit at the beginning of the period				1,434,800,000		1,600,500,000
R&W Development and Accretion of Discount	38,300,000		90,900,000	70,700,000		770,900,000
R&W Recovered				(292,600,000)	[2]	(898,100,000)	[2]
Future Net R&W Benefit at the end of the period	1,212,900,000		1,473,300,000	1,212,900,000		1,473,300,000
Gross R&W amounts recovered				311,400,000		1,015,000,000
Number of Risks as of the end of the period with R&W Benefit Recorded (in policies)	45	[3]		45	[3]			59	[3]
Debt Service of Policies with R&W Benefit Recorded as of the end of the period	4,292,500,000			4,292,500,000				7,479,900,000
Breakdown of the development and accretion amount
Inclusion of new deals with breaches of R&W during period	(5,000,000)		0	(5,000,000)		107,100,000
Change in recovery assumptions as the result of additional file review and recovery success	(10,000,000)		0	69,700,000		198,400,000
Estimated increase (decrease) in defaults that will result in additional breaches	50,900,000		(5,800,000)	(400,000)		34,000,000
Results of settlements	0		95,600,000	0		429,700,000
Accretion of discount on balance	2,400,000		1,100,000	6,400,000		1,700,000
Total	38,300,000		90,900,000	70,700,000		770,900,000
Additional information related to Representations and Warranties
Recovery payments received				(292,600,000)	[2]	(898,100,000)	[2]
Minimum
Financial guarantee obligations
Estimated Period of Recoveries on Transactions Backed by Heloc and Closed End Second Lien Loans Not Subject to Bank of America or Deutsche Bank	2 years
Maximum
Financial guarantee obligations
Estimated Period of Recoveries on Transactions Backed by Heloc and Closed End Second Lien Loans Not Subject to Bank of America or Deutsche Bank	4 years
Bank of America Agreement [Member]
Financial guarantee obligations
Estimated Benefit From Loan Repurchases Related to Breaches of R and W Included in Net Expected Loss Estimates	546,700,000			546,700,000
Deutsche Bank Agreement [Member]
Financial guarantee obligations
Estimated Benefit From Loan Repurchases Related to Breaches of R and W Included in Net Expected Loss Estimates	666,200,000			666,200,000
Prime first lien
Total
Benefit for R&W	4,000,000		2,900,000	4,000,000		2,900,000
Rollforward of Estimated Benefit from Recoveries of Representation and Warranty Breaches, Net of Reinsurance
Future Net R&W Benefit at the beginning of the period				3,000,000		1,100,000
R&W Development and Accretion of Discount				1,000,000		1,800,000
R&W Recovered				0	[2]	0	[2]
Future Net R&W Benefit at the end of the period	4,000,000		2,900,000	4,000,000		2,900,000
Number of Risks as of the end of the period with R&W Benefit Recorded (in policies)	1	[3]		1	[3]			1	[3]
Debt Service of Policies with R&W Benefit Recorded as of the end of the period	39,300,000			39,300,000				41,900,000
Breakdown of the development and accretion amount
Total				1,000,000		1,800,000
Additional information related to Representations and Warranties
Recovery payments received				0	[2]	0	[2]
Alt-A first lien
Total
Benefit for R&W	159,500,000		127,600,000	159,500,000		127,600,000
Rollforward of Estimated Benefit from Recoveries of Representation and Warranty Breaches, Net of Reinsurance
Future Net R&W Benefit at the beginning of the period				202,700,000		81,000,000
R&W Development and Accretion of Discount				21,000,000		46,600,000
R&W Recovered				(64,200,000)	[2]	0	[2]
Future Net R&W Benefit at the end of the period	159,500,000		127,600,000	159,500,000		127,600,000
Number of Risks as of the end of the period with R&W Benefit Recorded (in policies)	19	[3]		19	[3]			22	[3]
Debt Service of Policies with R&W Benefit Recorded as of the end of the period	1,492,900,000			1,492,900,000				1,732,600,000
Breakdown of the development and accretion amount
Total				21,000,000		46,600,000
Additional information related to Representations and Warranties
Recovery payments received				(64,200,000)	[2]	0	[2]
Total first lien
Financial guarantee obligations
Number of defaulted loan files reviewed	6,800			6,800
Outstanding par of defaulted loans reviewed	2,357,000,000			2,357,000,000
Number of loan files that breached one or more R&W	20,300			20,300
Amount of loans to be repurchased by providers	6,293,000,000			6,293,000,000
Total first lien | Bank of America Agreement [Member]
Additional information related to Representations and Warranties
Number of transactions insured executed as financial guarantees	20			20
Cumulative collateral losses	2,500,000,000			2,500,000,000
Cumulative projected collateral losses	5,000,000,000
Eligible assets in trust for payment of reimbursement	1,000,000,000			1,000,000,000
Total first lien | Bank of America Agreement [Member] | Maximum
Additional information related to Representations and Warranties
Cumulative collateral losses	6,600,000,000			6,600,000,000
Credit Default Swap [Member] | Bank of America Agreement [Member]
Additional information related to Representations and Warranties
Number of transactions insured executed as financial guarantees	1			1
Cumulative collateral losses	90,000,000			90,000,000
Cumulative projected collateral losses	200,000,000
Option ARM
Total
Benefit for R&W	697,100,000		711,200,000	697,100,000		711,200,000
Rollforward of Estimated Benefit from Recoveries of Representation and Warranty Breaches, Net of Reinsurance
Future Net R&W Benefit at the beginning of the period				713,900,000		309,300,000
R&W Development and Accretion of Discount				59,000,000		449,200,000
R&W Recovered				(75,800,000)	[2]	(47,300,000)	[2]
Future Net R&W Benefit at the end of the period	697,100,000		711,200,000	697,100,000		711,200,000
Number of Risks as of the end of the period with R&W Benefit Recorded (in policies)	10	[3]		10	[3]			12	[3]
Debt Service of Policies with R&W Benefit Recorded as of the end of the period	1,129,400,000			1,129,400,000				1,459,700,000
Breakdown of the development and accretion amount
Total				59,000,000		449,200,000
Additional information related to Representations and Warranties
Recovery payments received				(75,800,000)	[2]	(47,300,000)	[2]
Subprime
Total
Benefit for R&W	93,300,000		81,500,000	93,300,000		81,500,000
Rollforward of Estimated Benefit from Recoveries of Representation and Warranty Breaches, Net of Reinsurance
Future Net R&W Benefit at the beginning of the period				101,500,000		26,800,000
R&W Development and Accretion of Discount				(8,100,000)		54,700,000
R&W Recovered				(100,000)	[2]	0	[2]
Future Net R&W Benefit at the end of the period	93,300,000		81,500,000	93,300,000		81,500,000
Number of Risks as of the end of the period with R&W Benefit Recorded (in policies)	5	[3]		5	[3]			5	[3]
Debt Service of Policies with R&W Benefit Recorded as of the end of the period	842,000,000			842,000,000				905,800,000
Breakdown of the development and accretion amount
Total				(8,100,000)		54,700,000
Additional information related to Representations and Warranties
Recovery payments received				(100,000)	[2]	0	[2]
Second lien
Financial guarantee obligations
Number of defaulted loan files reviewed	34,200			34,200
Outstanding par of defaulted loans reviewed	2,593,000,000			2,593,000,000
Number of loan files that breached one or more R&W	11,000			11,000
Amount of loans to be repurchased by providers	812,000,000			812,000,000
Closed end second lien and HELOCs
Total
Benefit for R&W	136,900,000		239,700,000	136,900,000		239,700,000
Rollforward of Estimated Benefit from Recoveries of Representation and Warranty Breaches, Net of Reinsurance
Future Net R&W Benefit at the beginning of the period				223,800,000		178,200,000
R&W Development and Accretion of Discount				(2,000,000)		61,500,000
R&W Recovered				(84,900,000)	[2]	0	[2]
Future Net R&W Benefit at the end of the period	136,900,000		239,700,000	136,900,000		239,700,000
Number of Risks as of the end of the period with R&W Benefit Recorded (in policies)	4	[3]		4	[3]			4	[3]
Debt Service of Policies with R&W Benefit Recorded as of the end of the period	245,300,000			245,300,000				361,400,000
Breakdown of the development and accretion amount
Total				(2,000,000)		61,500,000
Additional information related to Representations and Warranties
Recovery payments received				(84,900,000)	[2]	0	[2]
HELOCs
Total
Benefit for R&W	122,100,000		310,400,000	122,100,000		310,400,000
Rollforward of Estimated Benefit from Recoveries of Representation and Warranty Breaches, Net of Reinsurance
Future Net R&W Benefit at the beginning of the period				189,900,000		1,004,100,000
R&W Development and Accretion of Discount				(200,000)		157,100,000
R&W Recovered				(67,600,000)	[2]	(850,800,000)	[2]
Future Net R&W Benefit at the end of the period	122,100,000		310,400,000	122,100,000		310,400,000
Number of Risks as of the end of the period with R&W Benefit Recorded (in policies)	6	[3],[4]		6	[3],[4]			15	[3],[4]
Debt Service of Policies with R&W Benefit Recorded as of the end of the period	543,600,000	[4]		543,600,000	[4]			2,978,500,000	[4]
Breakdown of the development and accretion amount
Total				(200,000)		157,100,000
Additional information related to Representations and Warranties
Recovery payments received				$ (67,600,000)	[2]	$ (850,800,000)	[2]

[1] The remaining benefit for R&W is not recorded on the balance sheet until the expected loss, net of R&W, exceeds unearned premium reserve.

[2] Gross amounts recovered were $311.4 million and $1,015.0 million in Six Months 2012 and 2011, respectively.

[3] A risk represents the aggregate of the financial guaranty policies that share the same revenue source for purposes of making debt service payments.

[4] The decline in number of HELOC risks and debt service relates to the final payment from Bank of America for covered HELOC transactions.