Expected Loss to be Paid - Net Expected Loss to be Paid and Net Economic Loss Development by Accounting Model (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	$ 1,169		$ 982		$ 677
Economic loss development after recoveries for R&W	(30)		56
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	584		493		282
Economic loss development after recoveries for R&W	(268)		(156)
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	595		620		432
Economic loss development after recoveries for R&W	(226)		(71)
RMBS [Member] | First Lien [Member] | 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	4		21		6
Economic loss development after recoveries for R&W	(16)		16
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	304		304		315
Economic loss development after recoveries for R&W	(144)		(81)
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)		(9)		(131)
Economic loss development after recoveries for R&W	(59)		(98)
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	303		304		242
Economic loss development after recoveries for R&W	(7)		92
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	(11)		(127)		(150)
Economic loss development after recoveries for R&W	(42)		(85)
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	8		(11)		(39)
Economic loss development after recoveries for R&W	3		6
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	(19)		(116)		(111)
Economic loss development after recoveries for R&W	(45)		(91)
TruPS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	23		51		27
Economic loss development after recoveries for R&W	(28)		7
Structured Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	218		120		312
Economic loss development after recoveries for R&W	96		(41)
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	303		264		7
Economic loss development after recoveries for R&W	183		239
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	45		57		52
Economic loss development after recoveries for R&W	(12)		17
Subtotal [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	1,173		985
Economic loss development after recoveries for R&W	(29)		66
Other Insurance Product Line [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	(4)		(3)		(3)
Economic loss development after recoveries for R&W	(1)		(10)
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	385		258
Economic loss development after recoveries for R&W	(280)		(130)
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	438		333
Economic loss development after recoveries for R&W	(150)		(69)
Financial Guarantee Accounted for as Insurance Contracts [Member] | RMBS [Member] | First Lien [Member] | 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		3
Economic loss development after recoveries for R&W	0		(1)
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	288		199
Economic loss development after recoveries for R&W	(87)		(54)
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	(15)		(18)
Economic loss development after recoveries for R&W	(48)		(62)
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	163		149
Economic loss development after recoveries for R&W	(15)		48
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	(53)		(75)
Economic loss development after recoveries for R&W	(130)		(61)
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	(27)		(34)
Economic loss development after recoveries for R&W	(2)		30
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	(26)		(41)
Economic loss development after recoveries for R&W	(128)		(91)
Financial Guarantee Accounted for as Insurance Contracts [Member] | TruPS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	1		3
Economic loss development after recoveries for R&W	(2)		0
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	255		161
Economic loss development after recoveries for R&W	97		(36)
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	303		264
Economic loss development after recoveries for R&W	183		239
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	45		55
Economic loss development after recoveries for R&W	(10)		16
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	989		741
Economic loss development after recoveries for R&W	(12)		89
Financial Guaranty Variable Interest Entities [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	126	[1]	60	[1]
Economic loss development after recoveries for R&W	85	[1]	(34)	[1]
Financial Guaranty Variable Interest Entities [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	88	[1]	110	[1]
Economic loss development after recoveries for R&W	(6)	[1]	1	[1]
Financial Guaranty Variable Interest Entities [Member] | RMBS [Member] | First Lien [Member] | 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]	0	[1]
Economic loss development after recoveries for R&W	0	[1]	0	[1]
Financial Guaranty Variable Interest Entities [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	17	[1]	31	[1]
Economic loss development after recoveries for R&W	(13)	[1]	5	[1]
Financial Guaranty Variable Interest Entities [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	0	[1]	(2)	[1]
Economic loss development after recoveries for R&W	1	[1]	(36)	[1]
Financial Guaranty Variable Interest Entities [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	71	[1]	81	[1]
Economic loss development after recoveries for R&W	6	[1]	32	[1]
Financial Guaranty Variable Interest Entities [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	38	[1]	(50)	[1]
Economic loss development after recoveries for R&W	91	[1]	(35)	[1]
Financial Guaranty Variable Interest Entities [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	31	[1]	25	[1]
Economic loss development after recoveries for R&W	8	[1]	(34)	[1]
Financial Guaranty Variable Interest Entities [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	[1]	(75)	[1]
Economic loss development after recoveries for R&W	83	[1]	(1)	[1]
Financial Guaranty Variable Interest Entities [Member] | TruPS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	0	[1]	0	[1]
Economic loss development after recoveries for R&W	0	[1]	0	[1]
Financial Guaranty Variable Interest Entities [Member] | Structured Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	0	[1]	0	[1]
Economic loss development after recoveries for R&W	0	[1]	0	[1]
Financial Guaranty Variable Interest Entities [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	0	[1]	0	[1]
Economic loss development after recoveries for R&W	0	[1]	0	[1]
Financial Guaranty Variable Interest Entities [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	0	[1]	0	[1]
Economic loss development after recoveries for R&W	0	[1]	0	[1]
Financial Guaranty Variable Interest Entities [Member] | Subtotal [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	126	[1]	60	[1]
Economic loss development after recoveries for R&W	85	[1]	(34)	[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	73	[2]	175	[2]
Economic loss development after recoveries for R&W	(73)	[2]	8	[2]
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	69	[2]	177	[2]
Economic loss development after recoveries for R&W	(70)	[2]	(3)	[2]
Financial Guarantee Accounted for as Credit Derivatives [Member] | RMBS [Member] | First Lien [Member] | 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]	18	[2]
Economic loss development after recoveries for R&W	(16)	[2]	17	[2]
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	(1)	[2]	74	[2]
Economic loss development after recoveries for R&W	(44)	[2]	(32)	[2]
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	(1)	[2]	11	[2]
Economic loss development after recoveries for R&W	(12)	[2]	0	[2]
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	69	[2]	74	[2]
Economic loss development after recoveries for R&W	2	[2]	12	[2]
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	4	[2]	(2)	[2]
Economic loss development after recoveries for R&W	(3)	[2]	11	[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	4	[2]	(2)	[2]
Economic loss development after recoveries for R&W	(3)	[2]	10	[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	0	[2]	0	[2]
Economic loss development after recoveries for R&W	0	[2]	1	[2]
Financial Guarantee Accounted for as Credit Derivatives [Member] | TruPS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	22	[2]	48	[2]
Economic loss development after recoveries for R&W	(26)	[2]	7	[2]
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	(37)	[2]	(41)	[2]
Economic loss development after recoveries for R&W	(1)	[2]	(5)	[2]
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	0	[2]	0	[2]
Economic loss development after recoveries for R&W	0	[2]	0	[2]
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	0	[2]	2	[2]
Economic loss development after recoveries for R&W	(2)	[2]	1	[2]
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	58	[2]	184	[2]
Economic loss development after recoveries for R&W	$ (102)	[2]	$ 11	[2]

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

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