Expected Losses to be Paid - Breaches of Representations and Warranties (Details) (USD $)	3 Months Ended	12 Months Ended					3 Months Ended										3 Months Ended						3 Months Ended								3 Months Ended																																															3 Months Ended			0 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Close ended second lien		Dec. 31, 2013 Close ended second lien		Mar. 31, 2014 Total first lien scenario		Mar. 31, 2013 Total first lien		Mar. 31, 2014 Alt-A first lien		Mar. 31, 2013 Alt-A first lien		Dec. 31, 2013 Alt-A first lien		Mar. 31, 2014 Option ARM		Mar. 31, 2013 Option ARM		Dec. 31, 2013 Option ARM		Mar. 31, 2014 First mortgage, subprime		Mar. 31, 2013 First mortgage, subprime		Dec. 31, 2013 First mortgage, subprime		Mar. 31, 2014 RMBS		Mar. 31, 2014 Prime first lien scenario		Mar. 31, 2013 Prime first lien		Mar. 31, 2014 Second lien		Mar. 31, 2013 Second lien		Mar. 31, 2014 Minimum Close ended second lien		Dec. 31, 2013 Minimum Close ended second lien		Mar. 31, 2014 Minimum Alt-A first lien		Dec. 31, 2013 Minimum Alt-A first lien		Mar. 31, 2014 Minimum Option ARM		Dec. 31, 2013 Minimum Option ARM		Mar. 31, 2014 Minimum First mortgage, subprime		Dec. 31, 2013 Minimum First mortgage, subprime		Mar. 31, 2014 Maximum Close ended second lien		Dec. 31, 2013 Maximum Close ended second lien		Mar. 31, 2014 Maximum Alt-A first lien		Dec. 31, 2013 Maximum Alt-A first lien		Mar. 31, 2014 Maximum Option ARM		Dec. 31, 2013 Maximum Option ARM		Mar. 31, 2014 Maximum First mortgage, subprime		Dec. 31, 2013 Maximum First mortgage, subprime		Mar. 31, 2014 Bank of America Agreement	Mar. 31, 2014 Bank of America Agreement Total first lien	Mar. 31, 2014 Bank of America Agreement Second lien	Mar. 31, 2014 Deutsche Bank Agreement	Mar. 31, 2014 UBS	May 06, 2013 UBS	Mar. 31, 2014 Other	Mar. 31, 2014 Uninsured tranches of covered transactions Deutsche Bank Agreement Transaction	Mar. 31, 2014 Uninsured tranches of covered transactions Deutsche Bank Agreement Maximum	Mar. 31, 2014 Covered Transactions Deutsche Bank Agreement	Oct. 10, 2013 Below Investment Grade [Member] Deutsche Bank Agreement
Guarantor Obligations [Line Items]
Amount of Liabilities Agreed Paid by Entities Providing R and Ws for Transactions Company Provided a Financial Guaranty	$ 3,697,000,000
Estimated Benefit From Loan Repurchases Related to Breaches of R and W Included in Net Expected Loss Estimates Under Agreements, Net of Reinsurance	384,000,000																																																																							195,000,000		100,000,000	33,000,000		56,000,000
Assets held under trust for reimbursement payment	874,000,000																																																																							585,000,000		142,000,000	147,000,000
Net par outstanding amount	5,804,000,000																																																																							1,023,000,000	1,335,000,000	1,649,000,000	778,000,000		1,019,000,000				294,000,000
Increase (Decrease) in Assets Held under Trust for Reimbursement Payment																																																																																	(60,000,000)
Cash Amount Already Received for Liabilities Agreed Paid by Entities Providing R and Ws for Transactions Company Provided a Financial Guaranty, Net of Reinsurance	2,497,000,000																																																																							490,000,000	968,000,000	235,000,000	410,000,000		394,000,000
Cash Amount Already Received for Liabilities Agreed Paid by Entities Providing R and Ws for Transactions Company Provided a Financial Guaranty	2,716,000,000
Plateau conditional default rate (as a percent)																																							6.70%	[1]	7.30%	[1]	2.30%	[1]	2.80%	[1]	3.80%	[1]	4.90%	[1]	5.90%	[1]	5.60%	[1]	15.50%	[1]	15.10%	[1]	18.40%	[1]	18.40%	[1]	16.80%	[1]	16.80%	[1]	16.30%	[1]	16.20%	[1]
Intermediate Conditional Default Rate																													5.00%														0.50%	[1]	0.60%	[1]	0.80%	[1]	1.00%	[1]	1.20%	[1]	1.10%	[1]					3.70%	[1]	3.70%	[1]	3.40%	[1]	3.40%	[1]	3.30%	[1]	3.20%	[1]
Final conditional default rate trended down to (as a percent)																																							3.50%	[1]	3.50%	[1]	0.10%	[1]	0.10%	[1]	0.20%	[1]	0.20%	[1]	0.30%	[1]	0.30%	[1]	9.10%	[1]	9.10%	[1]	0.90%	[1]	0.90%	[1]	0.80%	[1]	0.80%	[1]	0.80%	[1]	0.80%	[1]
Loss severity (as a percent)			98.00%	[1]	98.00%	[1]					65.00%	[1]			65.00%	[1]	65.00%	[1]			65.00%	[1]	90.00%	[1]			90.00%	[1]
Initial conditional prepayment rate (as a percent)																																							2.90%	[1]	3.10%	[1]	0.90%	[1]	0.00%	[1]	0.80%	[1]	0.40%	[1]	0.00%	[1]	0.00%	[1]	12.80%	[1]	12.00%	[1]	33.90%	[1]	34.20%	[1]	12.20%	[1]	13.10%	[1]	11.60%	[1]	15.70%	[1]
Final conditional prepayment rate (as a percent)			10.00%	[1]	10.00%	[1]					15.00%	[1]			15.00%	[1]	15.00%	[1]			15.00%	[1]	15.00%	[1]			15.00%	[1]							10.00%
Period from initial to final conditional prepayment rate (in months)		2 years 6 months					12 months
Current conditional prepayment rate used in alternate scenario for loss estimate (as a percent)							15.00%
Number of scenarios weighted in estimating expected losses																															5
Loss severity recovery period used to calculate potential change in loss estimate in even more stressful scenario (in years)							9 years
Period of decrease in conditional default rate until final rate is achieved (in months)																																			28 months
Number of scenarios where the recovery was faster than in base case							2
Decrease in the plateau period used to calculate potential change in loss estimate (in months)							6 months
Decreased plateau period used to calculate potential change in loss estimate (in months)							30 months
Estimated Benefit From Loan Repurchases Related to Breaches of R and W Included in Net Expected Loss Estimates Under Agreements	402,000,000
R&W recovered during period	384,000,000						38,000,000	[2]	62,000,000	[2]	8,000,000	[2]	8,000,000	[2]			30,000,000	[2]	54,000,000	[2]			0	[2]	0	[2]					0	[2]	0	[2]	1,000,000	[2]	27,000,000	[2]
Amount of Liabilities Agreed Paid by Entities Providing R and Ws for Transactions Company Provided a Financial Guaranty, Repurchase Amounts Prior to Settlement																													579,000,000	[3]
Estimated Benefit From Loan Repurchases Related to Breaches of R and W Included in Net Expected Loss Estimates	721,000,000
Financial Guaranty Insurance Contracts Principal Amount Already Covered Under Agreements But Company Projects Receiving Additional Amounts	773,000,000
Estimated Benefit From Loan Repurchases Related to Breaches of R and W Included in Net Expected Loss Estimates in Pursuit	337,000,000
Financial Guaranty Insurance Contracts Principal Amount Not Covered Under Agreements	1,379,000,000
Loss Sharing Percentage																																																																							80.00%					85.00%
Maximum Loss Up To Which Loss Sharing Percentage Applicable																																																																							6,600,000,000
Loss sharing percentage, first layer																																																																																80.00%
Maximum aggregate collateral losses up to which first layer of loss sharing will be applicable																																																																														141,000,000		319,000,000
Collateral Losses																																																																							3,900,000,000
Minimum losses at which second later of loss sharing percentage becomes applicable																																																																														161,000,000		389,000,000
Estimated Cumulative Collateral Losses																																																																							5,100,000,000								153,000,000
Minimum losses at which third layer of loss sharing percentage becomes applicable																																																																														185,000,000
Estimated Reimbursement Amount, Collateral Losses																																																																														24,000,000
Maximum Loss Up To Which Second Layer of Loss Sharing Percentage Applicable																																																																																600,000,000
Number of Transactions																																																																														8
Loss sharing percentage, second layer																																																																														60.00%		85.00%
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

[1] Represents variables for most heavily weighted scenario (the “base case”).

[2] Gross amounts recovered were $41 million and $92 million for First Quarter 2014 and 2013, respectively.

[3] These amounts were paid into the relevant RMBS transactions (rather than to the Company as in most settlements) and distributed in accordance with the priority of payments set out in the relevant transaction documents. Because the Company may insure only a portion of the capital structure of a transaction, such payments will not necessarily directly benefit the Company dollar-for-dollar, especially in first lien transactions.