Expected Loss to be Paid - Net Expected Loss to be Paid and Net Economic Loss Development by Accounting Model (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2015		Sep. 30, 2014	Sep. 30, 2015		Sep. 30, 2014		Jun. 30, 2015	Dec. 31, 2014		Jun. 30, 2014	Dec. 31, 2013
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		$ 1,307	[1]	$ 933	$ 1,307	[1]	$ 933		$ 1,510	$ 1,169	[1]	$ 1,035	$ 982
Economic loss development after recoveries for R&W		(3)		(63)	186		(28)
Subtotal [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		1,307			1,307					1,169
Economic loss development after recoveries for R&W		(3)		(63)	186		(28)
Public Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		730	[1]	384	730	[1]	384		657	348	[1]	391	321
Economic loss development after recoveries for R&W		91		1	321		101
Public Finance [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		687	[1]	333	687	[1]	333		613	303	[1]	339	264
Economic loss development after recoveries for R&W		92		2	327		107
Public Finance [Member] | Non United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		43	[1]	51	43	[1]	51		44	45	[1]	52	57
Economic loss development after recoveries for R&W		(1)		(1)	(6)		(6)
RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		335	[1]	381	335	[1]	381		524	584	[1]	476	493
Economic loss development after recoveries for R&W		(76)		(62)	(104)		(131)
RMBS [Member] | First Lien [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		309	[1]	534	309	[1]	534		521	595	[1]	602	620
Economic loss development after recoveries for R&W		(89)		(30)	(117)		(68)
RMBS [Member] | First Lien [Member] | Financing Receivable, Prime [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		0	[1]	10	0	[1]	10		1	4	[1]	11	21
Economic loss development after recoveries for R&W		0		(1)	(1)		(11)
RMBS [Member] | First Lien [Member] | Alt-A [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		46	[1]	248	46	[1]	248		265	304	[1]	301	304
Economic loss development after recoveries for R&W		(111)		(18)	(132)		(6)
RMBS [Member] | First Lien [Member] | Option ARM [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		(16)	[1]	(31)	(16)	[1]	(31)		(18)	(16)	[1]	(51)	(9)
Economic loss development after recoveries for R&W		(4)		0	(3)		(39)
RMBS [Member] | First Lien [Member] | Subprime [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		279	[1]	307	279	[1]	307		273	303	[1]	341	304
Economic loss development after recoveries for R&W		26		(11)	19		(12)
RMBS [Member] | Second Lien [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		26	[1]	(153)	26	[1]	(153)		3	(11)	[1]	(126)	(127)
Economic loss development after recoveries for R&W		13		(32)	13		(63)
RMBS [Member] | Second Lien [Member] | Closed-end [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		11	[1]	(5)	11	[1]	(5)		9	8	[1]	(9)	(11)
Economic loss development after recoveries for R&W		0		2	(2)		2
RMBS [Member] | Second Lien [Member] | HELOCs [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		15	[1]	(148)	15	[1]	(148)		(6)	(19)	[1]	(117)	(116)
Economic loss development after recoveries for R&W		13		(34)	15		(65)
Triple-X Life Insurance Transaction [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		98	[1]	92	98	[1]	92		165	161	[1]	90	75
Economic loss development after recoveries for R&W		1		3	8		21
Trust Preferred Securities (TruPS) [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		5	[1]	26	5	[1]	26		10	23	[1]	32	51
Economic loss development after recoveries for R&W		(5)		(5)	(18)		(24)	[2]
Student Loan [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		56	[1]	64	56	[1]	64		58	68	[1]	58	52
Economic loss development after recoveries for R&W		(2)		6	(7)		12	[2]
Other structured finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		83	[1]	(14)	83	[1]	(14)		96	(15)	[1]	(12)	(10)
Economic loss development after recoveries for R&W		(12)		(6)	(14)		(7)
Structured Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		577	[1]	549	577	[1]	549		$ 853	821	[1]	$ 644	$ 661
Economic loss development after recoveries for R&W		(94)		(64)	(135)		(129)
Financial Guarantee Accounted for as Insurance Contracts [Member] | Subtotal [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		1,145			1,145					989
Economic loss development after recoveries for R&W		67		(50)	286		(37)
Financial Guarantee Accounted for as Insurance Contracts [Member] | Public Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		730			730					348
Economic loss development after recoveries for R&W		90		1	326		102
Financial Guarantee Accounted for as Insurance Contracts [Member] | Public Finance [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		687			687					303
Economic loss development after recoveries for R&W		91		2	332		107
Financial Guarantee Accounted for as Insurance Contracts [Member] | Public Finance [Member] | Non United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		43			43					45
Economic loss development after recoveries for R&W		(1)		(1)	(6)		(5)
Financial Guarantee Accounted for as Insurance Contracts [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		237			237					385
Economic loss development after recoveries for R&W		(19)		(55)	(35)		(163)
Financial Guarantee Accounted for as Insurance Contracts [Member] | RMBS [Member] | First Lien [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		253			253					438
Economic loss development after recoveries for R&W		(30)		(9)	(47)		(25)
Financial Guarantee Accounted for as Insurance Contracts [Member] | RMBS [Member] | First Lien [Member] | Financing Receivable, Prime [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		2			2					2
Economic loss development after recoveries for R&W		0		(1)	0		0
Financial Guarantee Accounted for as Insurance Contracts [Member] | RMBS [Member] | First Lien [Member] | Alt-A [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		109			109					288
Economic loss development after recoveries for R&W		(44)		6	(54)		32
Financial Guarantee Accounted for as Insurance Contracts [Member] | RMBS [Member] | First Lien [Member] | Option ARM [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		(17)			(17)					(15)
Economic loss development after recoveries for R&W		(2)		7	(5)		(32)
Financial Guarantee Accounted for as Insurance Contracts [Member] | RMBS [Member] | First Lien [Member] | Subprime [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		159			159					163
Economic loss development after recoveries for R&W		16		(21)	12		(25)
Financial Guarantee Accounted for as Insurance Contracts [Member] | RMBS [Member] | Second Lien [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		(16)			(16)					(53)
Economic loss development after recoveries for R&W		11		(46)	12		(138)
Financial Guarantee Accounted for as Insurance Contracts [Member] | RMBS [Member] | Second Lien [Member] | Closed-end [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		(23)			(23)					(27)
Economic loss development after recoveries for R&W		(1)		2	(2)		0
Financial Guarantee Accounted for as Insurance Contracts [Member] | RMBS [Member] | Second Lien [Member] | HELOCs [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		7			7					(26)
Economic loss development after recoveries for R&W		12		(48)	14		(138)
Financial Guarantee Accounted for as Insurance Contracts [Member] | Triple-X Life Insurance Transaction [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		88			88					153
Economic loss development after recoveries for R&W		(1)		3	4		20
Financial Guarantee Accounted for as Insurance Contracts [Member] | Trust Preferred Securities (TruPS) [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		0			0					1
Economic loss development after recoveries for R&W		0		(1)	(1)		(2)
Financial Guarantee Accounted for as Insurance Contracts [Member] | Student Loan [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		56			56					68
Economic loss development after recoveries for R&W		(2)		6	(7)		12
Financial Guarantee Accounted for as Insurance Contracts [Member] | Other structured finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		34			34					34
Economic loss development after recoveries for R&W		(1)		(4)	(1)		(6)
Financial Guarantee Accounted for as Insurance Contracts [Member] | Structured Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W		415			415					641
Economic loss development after recoveries for R&W		(23)		(51)	(40)		(139)
Financial Guaranty Variable Interest Entities and Other [Member] | Subtotal [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[3]	135			135					122
Economic loss development after recoveries for R&W	[4]	9		21	10		74
Financial Guaranty Variable Interest Entities and Other [Member] | Public Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[3]	0			0					0
Economic loss development after recoveries for R&W	[4]	0		0	0		0
Financial Guaranty Variable Interest Entities and Other [Member] | Public Finance [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[3]	0			0					0
Economic loss development after recoveries for R&W	[4]	0		0	0		0
Financial Guaranty Variable Interest Entities and Other [Member] | Public Finance [Member] | Non United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[3]	0			0					0
Economic loss development after recoveries for R&W	[4]	0		0	0		0
Financial Guaranty Variable Interest Entities and Other [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[3]	117			117					126
Economic loss development after recoveries for R&W	[4]	9		21	10		75
Financial Guaranty Variable Interest Entities and Other [Member] | RMBS [Member] | First Lien [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[3]	79			79					88
Economic loss development after recoveries for R&W	[4]	7		6	9		(2)
Financial Guaranty Variable Interest Entities and Other [Member] | RMBS [Member] | First Lien [Member] | Financing Receivable, Prime [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[3]	0			0					0
Economic loss development after recoveries for R&W	[4]	0		0	0		0
Financial Guaranty Variable Interest Entities and Other [Member] | RMBS [Member] | First Lien [Member] | Alt-A [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[3]	16			16					17
Economic loss development after recoveries for R&W	[4]	0		(2)	(1)		(12)
Financial Guaranty Variable Interest Entities and Other [Member] | RMBS [Member] | First Lien [Member] | Option ARM [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[3]	0			0					0
Economic loss development after recoveries for R&W	[4]	0		0	0		1
Financial Guaranty Variable Interest Entities and Other [Member] | RMBS [Member] | First Lien [Member] | Subprime [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[3]	63			63					71
Economic loss development after recoveries for R&W	[4]	7		8	10		9
Financial Guaranty Variable Interest Entities and Other [Member] | RMBS [Member] | Second Lien [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[3]	38			38					38
Economic loss development after recoveries for R&W	[4]	2		15	1		77
Financial Guaranty Variable Interest Entities and Other [Member] | RMBS [Member] | Second Lien [Member] | Closed-end [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[3]	30			30					31
Economic loss development after recoveries for R&W	[4]	1		1	0		4
Financial Guaranty Variable Interest Entities and Other [Member] | RMBS [Member] | Second Lien [Member] | HELOCs [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[3]	8			8					7
Economic loss development after recoveries for R&W	[4]	1		14	1		73
Financial Guaranty Variable Interest Entities and Other [Member] | Triple-X Life Insurance Transaction [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[3]	0			0					0
Economic loss development after recoveries for R&W	[4]	0		0	0		0
Financial Guaranty Variable Interest Entities and Other [Member] | Trust Preferred Securities (TruPS) [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[3]	0			0					0
Economic loss development after recoveries for R&W	[4]	0		0	0		0
Financial Guaranty Variable Interest Entities and Other [Member] | Student Loan [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[3]	0			0					0
Economic loss development after recoveries for R&W	[4]	0		0	0		0
Financial Guaranty Variable Interest Entities and Other [Member] | Other structured finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[3]	18			18					(4)
Economic loss development after recoveries for R&W	[4]	0		0	0		(1)
Financial Guaranty Variable Interest Entities and Other [Member] | Structured Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[3]	135			135					122
Economic loss development after recoveries for R&W	[4]	9		21	10		74
Financial Guarantee Accounted for as Credit Derivatives [Member] | Subtotal [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[5]	27			27					58
Economic loss development after recoveries for R&W	[2]	(79)		(34)	(110)		(65)
Financial Guarantee Accounted for as Credit Derivatives [Member] | Public Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[5]	0			0					0
Economic loss development after recoveries for R&W	[2]	1		0	(5)		(1)
Financial Guarantee Accounted for as Credit Derivatives [Member] | Public Finance [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[5]	0			0					0
Economic loss development after recoveries for R&W	[2]	1		0	(5)		0
Financial Guarantee Accounted for as Credit Derivatives [Member] | Public Finance [Member] | Non United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[5]	0			0					0
Economic loss development after recoveries for R&W	[2]	0		0	0		(1)
Financial Guarantee Accounted for as Credit Derivatives [Member] | RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[5]	(19)			(19)					73
Economic loss development after recoveries for R&W	[2]	(66)		(28)	(79)		(43)
Financial Guarantee Accounted for as Credit Derivatives [Member] | RMBS [Member] | First Lien [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[5]	(23)			(23)					69
Economic loss development after recoveries for R&W	[2]	(66)		(27)	(79)		(41)
Financial Guarantee Accounted for as Credit Derivatives [Member] | RMBS [Member] | First Lien [Member] | Financing Receivable, Prime [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[5]	(2)			(2)					2
Economic loss development after recoveries for R&W	[2]	0		0	(1)		(11)
Financial Guarantee Accounted for as Credit Derivatives [Member] | RMBS [Member] | First Lien [Member] | Alt-A [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[5]	(79)			(79)					(1)
Economic loss development after recoveries for R&W	[2]	(67)		(22)	(77)		(26)
Financial Guarantee Accounted for as Credit Derivatives [Member] | RMBS [Member] | First Lien [Member] | Option ARM [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[5]	1			1					(1)
Economic loss development after recoveries for R&W	[2]	(2)		(7)	2		(8)
Financial Guarantee Accounted for as Credit Derivatives [Member] | RMBS [Member] | First Lien [Member] | Subprime [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[5]	57			57					69
Economic loss development after recoveries for R&W	[2]	3		2	(3)		4
Financial Guarantee Accounted for as Credit Derivatives [Member] | RMBS [Member] | Second Lien [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[5]	4			4					4
Economic loss development after recoveries for R&W	[2]	0		(1)	0		(2)
Financial Guarantee Accounted for as Credit Derivatives [Member] | RMBS [Member] | Second Lien [Member] | Closed-end [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[5]	4			4					4
Economic loss development after recoveries for R&W	[2]	0		(1)	0		(2)
Financial Guarantee Accounted for as Credit Derivatives [Member] | RMBS [Member] | Second Lien [Member] | HELOCs [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[5]	0			0					0
Economic loss development after recoveries for R&W	[2]	0		0	0		0
Financial Guarantee Accounted for as Credit Derivatives [Member] | Triple-X Life Insurance Transaction [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[5]	10			10					8
Economic loss development after recoveries for R&W	[2]	2		0	4		1
Financial Guarantee Accounted for as Credit Derivatives [Member] | Trust Preferred Securities (TruPS) [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[5]	5			5					22
Economic loss development after recoveries for R&W	[2]	(5)		(4)	(17)		(22)
Financial Guarantee Accounted for as Credit Derivatives [Member] | Student Loan [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[5]	0			0					0
Economic loss development after recoveries for R&W	[2]	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]
Net expected loss to be paid after recoveries for R&W	[5]	31			31					(45)
Economic loss development after recoveries for R&W	[2]	(11)		(2)	(13)		0
Financial Guarantee Accounted for as Credit Derivatives [Member] | Structured Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	[5]	27			27					$ 58
Economic loss development after recoveries for R&W	[2]	$ (80)		$ (34)	$ (105)		$ (64)

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

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

[3] Refer to Note 10, Consolidated Variable Interest Entities.

[4] Refer to Note 10, Consolidated Variable Interest Entities.

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