Expected Loss to be Paid - Narrative (Details)		1 Months Ended		3 Months Ended				9 Months Ended				12 Months Ended
		Dec. 31, 2014 USD ($) risk		Sep. 30, 2015 USD ($) risk Transaction		Jun. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) risk Transaction Curve Payment scenario		Sep. 30, 2014 USD ($)		Dec. 31, 2014 USD ($) risk		Oct. 31, 2015 USD ($)	Apr. 01, 2015 USD ($)	Mar. 31, 2015 USD ($)	Jun. 30, 2014 USD ($)	Dec. 31, 2013 USD ($)	May. 06, 2013	May. 31, 2012 USD ($)	Apr. 14, 2011 USD ($)
Schedule of Expected Losses to be Paid [Line Items]
Number of risks subject to R&W recovery | risk		29		28				28				29
Risks subject to R&W recovery, related net debt service amount		$ 2,100,000,000		$ 1,900,000,000				$ 1,900,000,000				$ 2,100,000,000
Number of risk subject to R&W recovery, terminated in next fiscal quarter | risk				1				1
Liability for unpaid claims and claims adjustment expense, net largest single loss		1,169,000,000	[1]	$ 1,307,000,000	[1]	$ 1,510,000,000	$ 933,000,000	$ 1,307,000,000	[1]	$ 933,000,000		1,169,000,000	[1]				$ 1,035,000,000	$ 982,000,000
Economic loss development after recoveries for R&W				(3,000,000)			(63,000,000)	186,000,000		(28,000,000)
Net par amount outstanding		403,729,000,000	[2]	372,361,000,000	[3],[4]			372,361,000,000	[3],[4]			403,729,000,000	[2]
Net Debt Service Outstanding		609,622,000,000		$ 556,381,000,000				$ 556,381,000,000				$ 609,622,000,000
Minimum [Member]
Schedule of Expected Losses to be Paid [Line Items]
Discount factor (as a percent)								0.00%				0.00%
Liquidation Rate for Bankruptcy Delinquent Category				10.00%				10.00%
Maximum [Member]
Schedule of Expected Losses to be Paid [Line Items]
Discount factor (as a percent)								3.34%				3.37%
Liquidation Rate for Bankruptcy Delinquent Category				100.00%				100.00%
Puerto Rico [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding		4,939,000,000		$ 5,091,000,000	[5]			$ 5,091,000,000	[5]			$ 4,939,000,000
Net Debt Service Outstanding				8,641,000,000				8,641,000,000
Gross par outstanding		6,035,000,000		5,798,000,000				5,798,000,000				6,035,000,000
RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Risks subject to R&W recovery, related net debt service amount terminated in next fiscal quarter				568,000,000				$ 568,000,000
RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Maximum number of payments behind to be considered performing borrower | Payment								1
Estimated benefit from loan repurchases related to breaches of R&W included in net expected loss estimates		317,000,000		198,000,000	[6]	225,000,000	578,000,000	$ 198,000,000	[6]	578,000,000		317,000,000				$ 2,000,000	651,000,000	712,000,000
Liability for unpaid claims and claims adjustment expense, net largest single loss		584,000,000	[1]	335,000,000	[1]	$ 524,000,000	381,000,000	335,000,000	[1]	381,000,000		584,000,000	[1]				476,000,000	493,000,000
Economic loss development after recoveries for R&W				(76,000,000)			(62,000,000)	(104,000,000)		(131,000,000)
Net par amount outstanding		$ 9,417,000,000		$ 8,400,000,000				$ 8,400,000,000				$ 9,417,000,000
RMBS [Member] | United States [Member] | Subprime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Final CPR	[7],[8]	15.00%		15.00%		15.00%		15.00%				15.00%
RMBS [Member] | United States [Member] | Option ARM [Member]
Schedule of Expected Losses to be Paid [Line Items]
Final CPR	[7],[8]	15.00%		15.00%		15.00%		15.00%				15.00%
RMBS [Member] | United States [Member] | Alt-A [Member]
Schedule of Expected Losses to be Paid [Line Items]
Final CPR	[7],[8]	15.00%										15.00%
RMBS [Member] | United States [Member] | Closed-end [Member]
Schedule of Expected Losses to be Paid [Line Items]
Final CPR	[9],[10]	15.00%				15.00%						15.00%
RMBS [Member] | United States [Member] | Minimum [Member] | Alt-A [Member]
Schedule of Expected Losses to be Paid [Line Items]
Final CPR	[7],[8]			15.00%		15.00%		15.00%
RMBS [Member] | United States [Member] | Minimum [Member] | HELOCs [Member]
Schedule of Expected Losses to be Paid [Line Items]
Final CPR	[9],[10]	15.00%		10.00%		10.00%		10.00%				15.00%
RMBS [Member] | United States [Member] | Minimum [Member] | Closed-end [Member]
Schedule of Expected Losses to be Paid [Line Items]
Final CPR	[9],[10]			15.00%				15.00%
RMBS [Member] | United States [Member] | Maximum [Member] | Alt-A [Member]
Schedule of Expected Losses to be Paid [Line Items]
Final CPR	[7],[8]			32.00%		27.70%		32.00%
RMBS [Member] | United States [Member] | Maximum [Member] | HELOCs [Member]
Schedule of Expected Losses to be Paid [Line Items]
Final CPR	[9],[10]	21.80%		15.00%		15.00%		15.00%				21.80%
RMBS [Member] | United States [Member] | Maximum [Member] | Closed-end [Member]
Schedule of Expected Losses to be Paid [Line Items]
Final CPR	[9],[10]			15.10%				15.10%
HELOCs [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Initial period for which borrower can pay only interest payments								10 years
Trust Preferred Securities (TruPS) [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss		$ 23,000,000	[1]	$ 5,000,000	[1]	$ 10,000,000	26,000,000	$ 5,000,000	[1]	26,000,000		$ 23,000,000	[1]				32,000,000	51,000,000
Economic loss development after recoveries for R&W				(5,000,000)			(5,000,000)	(18,000,000)		(24,000,000)	[11]
Net par amount outstanding		4,326,000,000		4,647,000,000				4,647,000,000				4,326,000,000
Triple-X Life Insurance Transaction [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss		161,000,000	[1]	98,000,000	[1]	165,000,000	92,000,000	98,000,000	[1]	92,000,000		161,000,000	[1]				90,000,000	75,000,000
Economic loss development after recoveries for R&W				1,000,000			3,000,000	8,000,000		21,000,000
Net par amount outstanding		3,133,000,000		2,750,000,000				2,750,000,000				3,133,000,000
Student Loan [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss		68,000,000	[1]	56,000,000	[1]	58,000,000	64,000,000	56,000,000	[1]	64,000,000		68,000,000	[1]				58,000,000	52,000,000
Economic loss development after recoveries for R&W				(2,000,000)			6,000,000	(7,000,000)		12,000,000	[11]
Net par amount outstanding		1,857,000,000		1,823,000,000				1,823,000,000				1,857,000,000
Other structured finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss		(15,000,000)	[1]	83,000,000	[1]	96,000,000	(14,000,000)	83,000,000	[1]	(14,000,000)		(15,000,000)	[1]				(12,000,000)	(10,000,000)
Economic loss development after recoveries for R&W				(12,000,000)			(6,000,000)	(14,000,000)		(7,000,000)
Net par amount outstanding		31,514,000,000		23,906,000,000				23,906,000,000				31,514,000,000
Collateralized Loan Obligations [Member]
Schedule of Expected Losses to be Paid [Line Items]
Increase in net expected losses to be paid after R&W in pessimistic scenario								120,000,000
Public Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss		348,000,000	[1]	730,000,000	[1]	657,000,000	384,000,000	730,000,000	[1]	384,000,000		348,000,000	[1]				391,000,000	321,000,000
Economic loss development after recoveries for R&W				91,000,000			1,000,000	321,000,000		101,000,000
Net Debt Service Outstanding		553,612,000,000		509,645,000,000				509,645,000,000				553,612,000,000
Public Finance [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss		303,000,000	[1]	687,000,000	[1]	613,000,000	333,000,000	687,000,000	[1]	333,000,000		303,000,000	[1]				339,000,000	264,000,000
Economic loss development after recoveries for R&W				92,000,000			2,000,000	327,000,000		107,000,000
Net par amount outstanding		$ 322,123,000,000	[2]	300,732,000,000	[3],[4]			300,732,000,000	[3],[4]			322,123,000,000	[2]
Public Finance [Member] | Puerto Rico [Member]
Schedule of Expected Losses to be Paid [Line Items]
Economic loss development after recoveries for R&W				92,000,000				327,000,000
Net par amount outstanding				5,100,000,000				5,100,000,000
Public Finance Stockton Pension Oblgiation Bonds [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding				115,000,000				115,000,000
Cancelled lease revenue bonds				40,000,000				40,000,000
Non-Infrastructure Public Finance [Member] | Spain [Member] | Sovereign and Sub Sovereign [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding				379,000,000				379,000,000
Gross par outstanding				474,000,000				474,000,000
Non-Infrastructure Public Finance [Member] | Portugal [Member] | Sovereign and Sub Sovereign [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding				89,000,000				89,000,000
Gross par outstanding				96,000,000				96,000,000
Non-Infrastructure Public Finance [Member] | Spain, Hungry and Portugal [Member] | Sovereign and Sub Sovereign [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss				41,000,000				41,000,000
Economic loss development after recoveries for R&W				(1,000,000)				(5,000,000)
Deutsche Bank [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Assets held under trust for reimbursement payment				71,000,000				71,000,000
City of Detroit [Member] | Public Finance [Member] | United States [Member] | Unlimited Tax General Obligation [Member]
Schedule of Expected Losses to be Paid [Line Items]
Guarantor obligation on un-exchanged balance, percent		15.50%
Net Debt Service Outstanding				23,000,000				23,000,000
Louisville Arena Authority [Member] | Public Finance [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding				337,000,000				337,000,000
BIG [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding		$ 18,247,000,000		17,611,000,000				17,611,000,000				18,247,000,000
BIG [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding		5,643,000,000		4,130,000,000				4,130,000,000				5,643,000,000
BIG [Member] | Trust Preferred Securities (TruPS) [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding		1,333,000,000		840,000,000				840,000,000				1,333,000,000
BIG [Member] | Triple-X Life Insurance Transaction [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding		598,000,000		216,000,000				216,000,000				598,000,000
BIG [Member] | Triple-X Life Insurance Transaction [Member] | Series A-1 Note [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding				382,500,000				382,500,000
BIG [Member] | Student Loan [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding		195,000,000		165,000,000				165,000,000				195,000,000
BIG [Member] | Other structured finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding		1,224,000,000		1,266,000,000				1,266,000,000				1,224,000,000
BIG [Member] | Public Finance [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding		7,850,000,000		9,480,000,000				9,480,000,000				7,850,000,000
BIG [Member] | Non-Infrastructure Public Finance [Member] | Hungary [Member] | Sovereign and Sub Sovereign [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding				279,000,000				279,000,000
Gross par outstanding				282,000,000				282,000,000
BIG [Member] | Parkway East [Member] | Public Finance [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding				21,000,000				21,000,000
Refinancing Risk on Infrastructure Transactions [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding				$ 3,000,000,000				$ 3,000,000,000
Financial insurance guaranty, infrastructure finance, number of possible claims requiring payment, gross before reinsurance | Transaction				2				2
Financial insurance guaranty, infrastructure finance, possible claims requiring payment, gross before reinsurance				$ 2,000,000,000				$ 2,000,000,000
Refinancing Risk on Infrastructure Transactions [Member] | Minimum [Member]
Schedule of Expected Losses to be Paid [Line Items]
Estimated years for recoveries of infrastructure transactions								10 years
Refinancing Risk on Infrastructure Transactions [Member] | Maximum [Member]
Schedule of Expected Losses to be Paid [Line Items]
Estimated years for recoveries of infrastructure transactions								35 years
First Lien [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Number of delinquent payments | Payment								2
Projected loss assumptions, CDR, plateau rate, projection period								36 months
Projected loss assumptions, Final CDR, Period for voluntary prepayments to continue								12 months
Intermediate conditional default rate (as a percent)				5.00%				5.00%
Number of scenarios weighted in estimating expected losses | scenario								5
Estimated benefit from loan repurchases related to breaches of R&W included in net expected loss estimates		232,000,000		$ 117,000,000	[6]	142,000,000	381,000,000	$ 117,000,000	[6]	381,000,000		232,000,000				1,000,000	509,000,000	569,000,000
Liability for unpaid claims and claims adjustment expense, net largest single loss		595,000,000	[1]	309,000,000	[1]	521,000,000	534,000,000	309,000,000	[1]	534,000,000		595,000,000	[1]				602,000,000	620,000,000
Economic loss development after recoveries for R&W				(89,000,000)			(30,000,000)	(117,000,000)		(68,000,000)
First Lien [Member] | RMBS [Member] | United States [Member] | Subprime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Estimated benefit from loan repurchases related to breaches of R&W included in net expected loss estimates		109,000,000		74,000,000	[6]	81,000,000	97,000,000	74,000,000	[6]	97,000,000		109,000,000				1,000,000	99,000,000	118,000,000
Liability for unpaid claims and claims adjustment expense, net largest single loss		303,000,000	[1]	279,000,000	[1]	273,000,000	307,000,000	279,000,000	[1]	307,000,000		303,000,000	[1]				341,000,000	304,000,000
Economic loss development after recoveries for R&W				26,000,000			(11,000,000)	19,000,000		(12,000,000)
Net par amount outstanding		4,051,000,000		3,759,000,000				3,759,000,000				4,051,000,000
First Lien [Member] | RMBS [Member] | United States [Member] | Financing Receivable, Prime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Estimated benefit from loan repurchases related to breaches of R&W included in net expected loss estimates		2,000,000		1,000,000	[6]	1,000,000	3,000,000	1,000,000	[6]	3,000,000		2,000,000				0	3,000,000	4,000,000
Liability for unpaid claims and claims adjustment expense, net largest single loss		4,000,000	[1]	0	[1]	1,000,000	10,000,000	0	[1]	10,000,000		4,000,000	[1]				11,000,000	21,000,000
Economic loss development after recoveries for R&W				0			(1,000,000)	(1,000,000)		(11,000,000)
Net par amount outstanding		471,000,000		465,000,000				465,000,000				471,000,000
First Lien [Member] | RMBS [Member] | United States [Member] | Option ARM [Member]
Schedule of Expected Losses to be Paid [Line Items]
Estimated benefit from loan repurchases related to breaches of R&W included in net expected loss estimates		15,000,000		(58,000,000)	[6]	(33,000,000)	78,000,000	(58,000,000)	[6]	78,000,000		15,000,000				0	144,000,000	173,000,000
Liability for unpaid claims and claims adjustment expense, net largest single loss		(16,000,000)	[1]	(16,000,000)	[1]	(18,000,000)	(31,000,000)	(16,000,000)	[1]	(31,000,000)		(16,000,000)	[1]				(51,000,000)	(9,000,000)
Economic loss development after recoveries for R&W				(4,000,000)			0	(3,000,000)		(39,000,000)
Net par amount outstanding		407,000,000		308,000,000				308,000,000				407,000,000
First Lien [Member] | RMBS [Member] | United States [Member] | Alt-A [Member]
Schedule of Expected Losses to be Paid [Line Items]
Estimated benefit from loan repurchases related to breaches of R&W included in net expected loss estimates		106,000,000		100,000,000	[6]	93,000,000	203,000,000	100,000,000	[6]	203,000,000		106,000,000				0	263,000,000	274,000,000
Liability for unpaid claims and claims adjustment expense, net largest single loss		304,000,000	[1]	46,000,000	[1]	$ 265,000,000	248,000,000	46,000,000	[1]	248,000,000		304,000,000	[1]				301,000,000	304,000,000
Economic loss development after recoveries for R&W				(111,000,000)			(18,000,000)	(132,000,000)		(6,000,000)
Net par amount outstanding		2,532,000,000		$ 2,189,000,000				$ 2,189,000,000				$ 2,532,000,000
First Lien [Member] | Base Scenario [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Final CPR				15.00%				15.00%
Projected loss assumptions, CDR, plateau rate, projection period								36 months
Period from plateau to intermediate conditional default rate (in months)								12 months
Period of constant intermediate conditional default rate (in months)								36 months
Intermediate conditional default rate as a percentage of plateau conditional default rate								20.00%
Final conditional default rate as a percentage of plateau conditional default rate								5.00%
Final conditional default rate, shortened term						3 months						9 months
Default from delinquentor rate, term								36 months
Guarantor Obligations, Default Period Currently Performing								36 months
Projected loss assumptions, loss severity, subsequent period								18 months
Estimated loss severity rate, one through six months (as a percent)								18 months
Loss severity (as a percent)				40.00%				40.00%
Projected loss assumptions, period to reach final loss severity rate								2 years 6 months
Projected loss assumptions, Final CDR, Period for voluntary prepayments to continue								7 years 9 months
First Lien [Member] | Somewhat Stressful Environment [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, CDR, plateau rate, projection period								42 months
Projected loss assumptions, period to reach final loss severity rate								4 years 6 months
Increase in the plateau period used to calculate potential change in loss estimate (in months)								6 months
Projected loss assumptions, prior period to reach final loss severity rate								2 years 6 months
First Lien [Member] | Somewhat Stressful Environment [Member] | RMBS [Member] | United States [Member] | Subprime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, increase (decrease) in expected loss to be paid, net								$ 49,000,000
First Lien [Member] | Somewhat Stressful Environment [Member] | RMBS [Member] | United States [Member] | Financing Receivable, Prime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, increase (decrease) in expected loss to be paid, net								$ 1,000,000
First Lien [Member] | Somewhat Stressful Environment [Member] | RMBS [Member] | United States [Member] | Option Adjustable Rate Mortgage and Alt-A Mortgage [Member]
Schedule of Expected Losses to be Paid [Line Items]
Loss severity (as a percent)				45.00%				45.00%
First Lien [Member] | Somewhat Stressful Environment [Member] | RMBS [Member] | United States [Member] | Option ARM [Member]
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, increase (decrease) in expected loss to be paid, net								$ 5,000,000
First Lien [Member] | Somewhat Stressful Environment [Member] | RMBS [Member] | United States [Member] | Alt-A [Member]
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, increase (decrease) in expected loss to be paid, net								$ 13,000,000
First Lien [Member] | Somewhat Stressful Environment [Member] | Subprime [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Loss severity (as a percent)				60.00%				60.00%
First Lien [Member] | More Stressful Environment [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Period from plateau to intermediate conditional default rate (in months)								15 months
Projected loss assumptions, period to reach final loss severity rate								9 years
First Lien [Member] | More Stressful Environment [Member] | RMBS [Member] | United States [Member] | Subprime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, increase (decrease) in expected loss to be paid, net								$ 69,000,000
First Lien [Member] | More Stressful Environment [Member] | RMBS [Member] | United States [Member] | Financing Receivable, Prime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, increase (decrease) in expected loss to be paid, net								4,000,000
First Lien [Member] | More Stressful Environment [Member] | RMBS [Member] | United States [Member] | Option ARM [Member]
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, increase (decrease) in expected loss to be paid, net								12,000,000
First Lien [Member] | More Stressful Environment [Member] | RMBS [Member] | United States [Member] | Alt-A [Member]
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, increase (decrease) in expected loss to be paid, net								33,000,000
First Lien [Member] | Somewhat Less Stressful Environment [Member] | RMBS [Member] | United States [Member] | Subprime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, increase (decrease) in expected loss to be paid, net								(8,000,000)
First Lien [Member] | Somewhat Less Stressful Environment [Member] | RMBS [Member] | United States [Member] | Financing Receivable, Prime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, increase (decrease) in expected loss to be paid, net								(40,000)
First Lien [Member] | Somewhat Less Stressful Environment [Member] | RMBS [Member] | United States [Member] | Option ARM [Member]
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, increase (decrease) in expected loss to be paid, net								(14,000,000)
First Lien [Member] | Somewhat Less Stressful Environment [Member] | RMBS [Member] | United States [Member] | Alt-A [Member]
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, increase (decrease) in expected loss to be paid, net								$ (1,000,000)
First Lien [Member] | Least Stressful Environment [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, CDR, plateau rate, projection period								30 months
Period from plateau to intermediate conditional default rate (in months)								9 months
Decrease in the plateau period used to calculate potential change in loss estimate (in months)								6 months
First Lien [Member] | Least Stressful Environment [Member] | RMBS [Member] | United States [Member] | Subprime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, increase (decrease) in expected loss to be paid, net								$ (36,000,000)
First Lien [Member] | Least Stressful Environment [Member] | RMBS [Member] | United States [Member] | Financing Receivable, Prime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, increase (decrease) in expected loss to be paid, net								(200,000)
First Lien [Member] | Least Stressful Environment [Member] | RMBS [Member] | United States [Member] | Option ARM [Member]
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, increase (decrease) in expected loss to be paid, net								(22,000,000)
First Lien [Member] | Least Stressful Environment [Member] | RMBS [Member] | United States [Member] | Alt-A [Member]
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, increase (decrease) in expected loss to be paid, net								(13,000,000)
First Lien [Member] | Bank of America [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Agreed reimbursement of R&W, percentage																					80.00%
Maximum loss up to which loss sharing percentage applicable																					$ 6,600,000,000
Collateral losses				$ 4,300,000,000				4,300,000,000
First Lien [Member] | Bank of America [Member] | Base Scenario [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Collateral losses				5,200,000,000				5,200,000,000
Assets held under trust for reimbursement payment				551,000,000				551,000,000
First Lien [Member] | UBS [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Agreed reimbursement of R&W, percentage																			85.00%
Assets held under trust for reimbursement payment				62,000,000				62,000,000
First Lien [Member] | BIG [Member] | RMBS [Member] | United States [Member] | Subprime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding		1,575,000,000		1,336,000,000				1,336,000,000				$ 1,575,000,000
First Lien [Member] | BIG [Member] | RMBS [Member] | United States [Member] | Financing Receivable, Prime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding		353,000,000		312,000,000				312,000,000				353,000,000
First Lien [Member] | BIG [Member] | RMBS [Member] | United States [Member] | Option ARM [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding		183,000,000		151,000,000				151,000,000				183,000,000
First Lien [Member] | BIG [Member] | RMBS [Member] | United States [Member] | Alt-A [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding		1,841,000,000		821,000,000				$ 821,000,000				1,841,000,000
Second Lien [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Period from plateau to intermediate conditional default rate (in months)								28 months
Period of loan default estimate								5 months
Number of preceding months average liquidation rates used to estimate loan default rate								6 months
Projected loss assumptions, period of consistent conditional default rate								6 months
Stress period (in months)								34 months
Number of months of delinquent data								5 months
Period of constant conditional default rate (in months)								1 month
Conditional prepayment rate base case, average number of quarters								3 months
Number of conditional default rate curves modeled in estimating losses | Curve								5
Estimated benefit from loan repurchases related to breaches of R&W included in net expected loss estimates		85,000,000		81,000,000	[6]	$ 83,000,000	197,000,000	$ 81,000,000	[6]	197,000,000		85,000,000				1,000,000	142,000,000	143,000,000
Liability for unpaid claims and claims adjustment expense, net largest single loss		(11,000,000)	[1]	26,000,000	[1]	3,000,000	(153,000,000)	26,000,000	[1]	(153,000,000)		(11,000,000)	[1]				(126,000,000)	(127,000,000)
Economic loss development after recoveries for R&W				13,000,000			(32,000,000)	13,000,000		(63,000,000)
Second Lien [Member] | RMBS [Member] | United States [Member] | HELOCs [Member]
Schedule of Expected Losses to be Paid [Line Items]
Estimated benefit from loan repurchases related to breaches of R&W included in net expected loss estimates		0		0	[6]	0	108,000,000	0	[6]	108,000,000		0				0	49,000,000	45,000,000
Liability for unpaid claims and claims adjustment expense, net largest single loss		(19,000,000)	[1]	15,000,000	[1]	(6,000,000)	(148,000,000)	15,000,000	[1]	(148,000,000)		(19,000,000)	[1]				(117,000,000)	(116,000,000)
Economic loss development after recoveries for R&W				13,000,000			(34,000,000)	15,000,000		(65,000,000)
Net par amount outstanding		1,738,000,000		1,476,000,000				1,476,000,000				1,738,000,000
Second Lien [Member] | RMBS [Member] | United States [Member] | Closed-end [Member]
Schedule of Expected Losses to be Paid [Line Items]
Estimated benefit from loan repurchases related to breaches of R&W included in net expected loss estimates		85,000,000		81,000,000	[6]	83,000,000	89,000,000	81,000,000	[6]	89,000,000		85,000,000				$ 1,000,000	93,000,000	98,000,000
Liability for unpaid claims and claims adjustment expense, net largest single loss		8,000,000	[1]	11,000,000	[1]	$ 9,000,000	(5,000,000)	11,000,000	[1]	(5,000,000)		8,000,000	[1]				$ (9,000,000)	$ (11,000,000)
Economic loss development after recoveries for R&W				0			2,000,000	(2,000,000)		2,000,000
Net par amount outstanding		$ 218,000,000		$ 203,000,000				$ 203,000,000				$ 218,000,000
Second Lien [Member] | RMBS [Member] | United States [Member] | Home Equity Line of Credit and Closed-end Mortgage [Member]
Schedule of Expected Losses to be Paid [Line Items]
Final CPR		15.00%		15.00%		15.00%		15.00%				15.00%
Second Lien [Member] | HELOCs [Member] | Maximum [Member]
Schedule of Expected Losses to be Paid [Line Items]
Loss recovery assumption (as a percent)		10.00%		10.00%		10.00%		10.00%				10.00%
Second Lien [Member] | Base Scenario [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Period from plateau to intermediate conditional default rate (in months)								28 months
Stress period (in months)								34 months
Period of constant conditional default rate (in months)								6 months
Second Lien [Member] | Base Scenario One [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, CDR, plateau rate, projection period								8 months
Period from plateau to intermediate conditional default rate (in months)								31 months
Stress period (in months)								39 months
Increase in conditional default rate ramp down period								3 months
Second Lien [Member] | Base Scenario One [Member] | RMBS [Member] | United States [Member] | HELOCs [Member]
Schedule of Expected Losses to be Paid [Line Items]
Change in estimate for increased conditional default rate plateau period								$ 37,000,000
Second Lien [Member] | Base Scenario One [Member] | RMBS [Member] | United States [Member] | Closed-end [Member]
Schedule of Expected Losses to be Paid [Line Items]
Change in estimate for decreased conditional default rate ramp down period								$ 1,000,000
Second Lien [Member] | Based Scenario Two [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Stress period (in months)								29 months
Period of constant conditional default rate (in months)								4 months
Change in estimate for decreased prepayment rate, Percent								10.00%
Decreased conditional default rate ramp down period								25 months
Second Lien [Member] | Based Scenario Two [Member] | RMBS [Member] | United States [Member] | HELOCs [Member]
Schedule of Expected Losses to be Paid [Line Items]
Change in estimate for decreased conditional default rate ramp down period								$ 36,000,000
Second Lien [Member] | Based Scenario Two [Member] | RMBS [Member] | United States [Member] | Closed-end [Member]
Schedule of Expected Losses to be Paid [Line Items]
Change in estimate for decreased conditional default rate ramp down period								600,000
Second Lien [Member] | Guarantor Obligations, Group One [Member] | Deutsche Bank [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Maximum aggregate collateral losses up to which first layer of loss sharing will be applicable				$ 319,000,000				319,000,000												$ 319,000,000
Loss sharing percentage, first layer																				80.00%
Second Lien [Member] | Guarantor Obligations, Group Two [Member] | Deutsche Bank [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Maximum aggregate collateral losses up to which first layer of loss sharing will be applicable				$ 389,000,000				$ 389,000,000
Loss sharing percentage, first layer				85.00%				85.00%
Second Lien [Member] | Guarantor Obligations, Group Two [Member] | Deutsche Bank [Member] | RMBS [Member] | United States [Member] | Maximum [Member]
Schedule of Expected Losses to be Paid [Line Items]
Maximum aggregate collateral losses up to which first layer of loss sharing will be applicable				$ 600,000,000				$ 600,000,000
Second Lien [Member] | BIG [Member] | RMBS [Member] | United States [Member] | HELOCs [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding		$ 1,557,000,000		1,382,000,000				1,382,000,000				$ 1,557,000,000
Second Lien [Member] | BIG [Member] | RMBS [Member] | United States [Member] | Closed-end [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding		134,000,000		128,000,000				128,000,000				134,000,000
Other Assets [Member]
Schedule of Expected Losses to be Paid [Line Items]
Office building, carrying value				29,000,000				29,000,000
Southern District of Mississippi Vs Madison County, Mississippi [Member] | Parkway East [Member] | Public Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding				21,000,000				$ 21,000,000
Payment time period on annual debt service								2 years
Radian [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding	[3],[4]			12,400,000,000				$ 12,400,000,000
Radian [Member] | Other structured finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss															$ 101,000,000
Radian [Member] | Public Finance [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss															$ 81,000,000
Healthcare [Member] | Public Finance [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding				15,400,000,000				15,400,000,000
Healthcare [Member] | BIG [Member] | Public Finance [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding				351,000,000				351,000,000
Healthcare [Member] | Radian [Member] | BIG [Member] | Public Finance [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net par amount outstanding				301,000,000				301,000,000
Financial Guarantee Accounted for as Credit Derivatives [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss	[12]	73,000,000		(19,000,000)				(19,000,000)				73,000,000
Economic loss development after recoveries for R&W	[11]			(66,000,000)			(28,000,000)	$ (79,000,000)		(43,000,000)
Financial Guarantee Accounted for as Credit Derivatives [Member] | Trust Preferred Securities (TruPS) [Member]
Schedule of Expected Losses to be Paid [Line Items]
Percentage of installment premiums denominated in currencies other than the U.S. dollar								78.00%
Liability for unpaid claims and claims adjustment expense, net largest single loss	[12]	22,000,000		5,000,000				$ 5,000,000				22,000,000
Economic loss development after recoveries for R&W	[11]			(5,000,000)			(4,000,000)	(17,000,000)		(22,000,000)
Financial Guarantee Accounted for as Credit Derivatives [Member] | Triple-X Life Insurance Transaction [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss	[12]	8,000,000		10,000,000				10,000,000				8,000,000
Economic loss development after recoveries for R&W	[11]			2,000,000			0	4,000,000		1,000,000
Financial Guarantee Accounted for as Credit Derivatives [Member] | Student Loan [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss	[12]	0		0				0				0
Economic loss development after recoveries for R&W	[11]			0			0	0		0
Financial Guarantee Accounted for as Credit Derivatives [Member] | Other structured finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss	[12]	(45,000,000)		31,000,000				31,000,000				(45,000,000)
Economic loss development after recoveries for R&W	[11]			(11,000,000)			(2,000,000)	(13,000,000)		0
Financial Guarantee Accounted for as Credit Derivatives [Member] | Public Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss	[12]	0		0				0				0
Economic loss development after recoveries for R&W	[11]			1,000,000			0	(5,000,000)		(1,000,000)
Financial Guarantee Accounted for as Credit Derivatives [Member] | Public Finance [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss	[12]	0		0				0				0
Economic loss development after recoveries for R&W	[11]			1,000,000			0	(5,000,000)		0
Financial Guarantee Accounted for as Credit Derivatives [Member] | First Lien [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss	[12]	69,000,000		(23,000,000)				(23,000,000)				69,000,000
Economic loss development after recoveries for R&W	[11]			(66,000,000)			(27,000,000)	(79,000,000)		(41,000,000)
Financial Guarantee Accounted for as Credit Derivatives [Member] | First Lien [Member] | RMBS [Member] | United States [Member] | Subprime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss	[12]	69,000,000		57,000,000				57,000,000				69,000,000
Economic loss development after recoveries for R&W	[11]			3,000,000			2,000,000	(3,000,000)		4,000,000
Financial Guarantee Accounted for as Credit Derivatives [Member] | First Lien [Member] | RMBS [Member] | United States [Member] | Financing Receivable, Prime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss	[12]	2,000,000		(2,000,000)				(2,000,000)				2,000,000
Economic loss development after recoveries for R&W	[11]			0			0	(1,000,000)		(11,000,000)
Financial Guarantee Accounted for as Credit Derivatives [Member] | First Lien [Member] | RMBS [Member] | United States [Member] | Option ARM [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss	[12]	(1,000,000)		1,000,000				1,000,000				(1,000,000)
Economic loss development after recoveries for R&W	[11]			(2,000,000)			(7,000,000)	2,000,000		(8,000,000)
Financial Guarantee Accounted for as Credit Derivatives [Member] | First Lien [Member] | RMBS [Member] | United States [Member] | Alt-A [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss	[12]	(1,000,000)		(79,000,000)				(79,000,000)				(1,000,000)
Economic loss development after recoveries for R&W	[11]			(67,000,000)			(22,000,000)	(77,000,000)		(26,000,000)
Financial Guarantee Accounted for as Credit Derivatives [Member] | Second Lien [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss	[12]	4,000,000		4,000,000				4,000,000				4,000,000
Economic loss development after recoveries for R&W	[11]			0			(1,000,000)	0		(2,000,000)
Financial Guarantee Accounted for as Credit Derivatives [Member] | Second Lien [Member] | RMBS [Member] | United States [Member] | HELOCs [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss	[12]	0		0				0				0
Economic loss development after recoveries for R&W	[11]			0			0	0		0
Financial Guarantee Accounted for as Credit Derivatives [Member] | Second Lien [Member] | RMBS [Member] | United States [Member] | Closed-end [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liability for unpaid claims and claims adjustment expense, net largest single loss	[12]	$ 4,000,000		4,000,000				4,000,000				$ 4,000,000
Economic loss development after recoveries for R&W	[11]			$ 0			$ (1,000,000)	$ 0		$ (2,000,000)
Subsequent Event [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Amount of liabilities agreed to be paid by entities providing R&W for transaction in which the Company provided insurance														$ 4,200,000,000

[1] Includes expected LAE to be paid of $13 million as of September 30, 2015 and $16 million as of December 31, 2014.

[2] Excludes $1.3 billion of loss mitigation securities insured and held by the Company as of December 31, 2014, which are primarily BIG.

[3] Excludes $1.6 billion of loss mitigation securities insured and held by the Company as of September 30, 2015, which are primarily BIG.

[4] The September 30, 2015 amounts include $12.4 billion of net par acquired from Radian Asset.

[5] $385 million acquired in the Radian Asset Acquisition, of which $21 million was of PREPA and $166 million

[6] See the section "Breaches of Representations and Warranties" below for eligible assets held in trust.

[7] For transactions where the initial CPR is higher than the final CPR, the initial CPR is held constant and the final CPR is not used.

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

[9] For transactions where the initial CPR is higher than the final CPR, the initial CPR is held constant and the final CPR is not used.

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

[11] Refer to Note 9, Financial Guaranty Contracts Accounted for as Credit Derivatives.

[12] Refer to Note 9, Financial Guaranty Contracts Accounted for as Credit Derivatives.