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	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014		Dec. 31, 2013
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	$ 1,154	[1]	$ 984	[1]	$ 1,169	[1]	$ 982	[1]
Economic loss development after recoveries for R&W	(3)		12
Subtotal [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	1,153	[1]	988	[1]	1,173	[1]	985	[1]
Economic loss development after recoveries for R&W	(2)		13
Public Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	352	[1]	338	[1]	348	[1]	321	[1]
Economic loss development after recoveries for R&W	6		23
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	310	[1]	281	[1]	303	[1]	264	[1]
Economic loss development after recoveries for R&W	9		23
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	42	[1]	57	[1]	45	[1]	57	[1]
Economic loss development after recoveries for R&W	(3)		0
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	570	[1]	480	[1]	584	[1]	493	[1]
Economic loss development after recoveries for R&W	4		(10)
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	569	[1]	593	[1]	595	[1]	620	[1]
Economic loss development after recoveries for R&W	(2)		(17)
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	3	[1]	18	[1]	4	[1]	21	[1]
Economic loss development after recoveries for R&W	0		(3)
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	289	[1]	308	[1]	304	[1]	304	[1]
Economic loss development after recoveries for R&W	(5)		8
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]	(28)	[1]	(16)	[1]	(9)	[1]
Economic loss development after recoveries for R&W	4		(15)
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	293	[1]	295	[1]	303	[1]	304	[1]
Economic loss development after recoveries for R&W	(1)		(7)
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	1	[1]	(113)	[1]	(11)	[1]	(127)	[1]
Economic loss development after recoveries for R&W	6		7
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]	(4)	[1]	8	[1]	(11)	[1]
Economic loss development after recoveries for R&W	1		5
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	(10)	[1]	(109)	[1]	(19)	[1]	(116)	[1]
Economic loss development after recoveries for R&W	5		2
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	165	[1]	87	[1]	161	[1]	75	[1]
Economic loss development after recoveries for R&W	5		13
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	14	[1]	32	[1]	23	[1]	51	[1]
Economic loss development after recoveries for R&W	(9)		(19)	[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	52	[1]	51	[1]	57	[1]	45	[1]
Economic loss development after recoveries for R&W	(8)		6
Structured Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	801	[1]	650	[1]	825	[1]	664	[1]
Economic loss development after recoveries for R&W	(8)		(10)
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	1	[1]	(4)	[1]	(4)	[1]	(3)	[1]
Economic loss development after recoveries for R&W	(1)		(1)
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				989
Economic loss development after recoveries for R&W	12		(23)
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	352				348
Economic loss development after recoveries for R&W	6		23
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	310				303
Economic loss development after recoveries for R&W	9		23
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	42				45
Economic loss development after recoveries for R&W	(3)		0
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	382				385
Economic loss development after recoveries for R&W	8		(62)
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	421				438
Economic loss development after recoveries for R&W	0		(5)
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	3				2
Economic loss development after recoveries for R&W	1		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	278				288
Economic loss development after recoveries for R&W	2		19
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)				(15)
Economic loss development after recoveries for R&W	1		(16)
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	157				163
Economic loss development after recoveries for R&W	(4)		(8)
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	(39)				(53)
Economic loss development after recoveries for R&W	8		(57)
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	(24)				(27)
Economic loss development after recoveries for R&W	1		(1)
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	(15)				(26)
Economic loss development after recoveries for R&W	7		(56)
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	157				153
Economic loss development after recoveries for R&W	4		13
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				1
Economic loss development after recoveries for R&W	(1)		(1)
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	98				102
Economic loss development after recoveries for R&W	(5)		4
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	637				641
Economic loss development after recoveries for R&W	6		(46)
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	122	[3]			126	[3]
Economic loss development after recoveries for R&W	3	[3]	47	[3]
Financial Guaranty Variable Interest Entities [Member] | Public Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	0				0	[3]
Economic loss development after recoveries for R&W	0	[3]	0	[3]
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	[3]			0	[3]
Economic loss development after recoveries for R&W	0	[3]	0	[3]
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	[3]			0	[3]
Economic loss development after recoveries for R&W	0	[3]	0	[3]
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	122	[3]			126	[3]
Economic loss development after recoveries for R&W	3	[3]	47	[3]
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	86	[3]			88	[3]
Economic loss development after recoveries for R&W	4	[3]	(13)	[3]
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	[3]			0	[3]
Economic loss development after recoveries for R&W	0	[3]	0	[3]
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	[3]			17	[3]
Economic loss development after recoveries for R&W	0	[3]	(12)	[3]
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	[3]			0	[3]
Economic loss development after recoveries for R&W	0	[3]	1	[3]
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	69	[3]			71	[3]
Economic loss development after recoveries for R&W	4	[3]	(2)	[3]
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	36	[3]			38	[3]
Economic loss development after recoveries for R&W	(1)	[3]	60	[3]
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	[3]			31	[3]
Economic loss development after recoveries for R&W	1	[3]	2	[3]
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	5	[3]			7	[3]
Economic loss development after recoveries for R&W	(2)	[3]	58	[3]
Financial Guaranty Variable Interest Entities [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	0	[3]			0	[3]
Economic loss development after recoveries for R&W	0	[3]	0	[3]
Financial Guaranty Variable Interest Entities [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	[3]			0	[3]
Economic loss development after recoveries for R&W	0	[3]	0	[3]
Financial Guaranty Variable Interest Entities [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	0	[3]			0	[3]
Economic loss development after recoveries for R&W	0	[3]	0	[3]
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	122	[3]			126	[3]
Economic loss development after recoveries for R&W	3	[3]	47	[3]
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	42	[2]			58	[2]
Economic loss development after recoveries for R&W	(17)	[2]	(11)	[2]
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	0				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] | 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]			0	[2]
Economic loss development after recoveries for R&W	0	[2]	0	[2]
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	66	[2]			73	[2]
Economic loss development after recoveries for R&W	(7)	[2]	5	[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	62	[2]			69	[2]
Economic loss development after recoveries for R&W	(6)	[2]	1	[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	0	[2]			2	[2]
Economic loss development after recoveries for R&W	(1)	[2]	(3)	[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	(6)	[2]			(1)	[2]
Economic loss development after recoveries for R&W	(7)	[2]	1	[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]			(1)	[2]
Economic loss development after recoveries for R&W	3	[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	67	[2]			69	[2]
Economic loss development after recoveries for R&W	(1)	[2]	3	[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]			4	[2]
Economic loss development after recoveries for R&W	(1)	[2]	4	[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]			4	[2]
Economic loss development after recoveries for R&W	(1)	[2]	4	[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]	0	[2]
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	8	[2]			8	[2]
Economic loss development after recoveries for R&W	1	[2]	0	[2]
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	14	[2]			22	[2]
Economic loss development after recoveries for R&W	(8)	[2]	(18)	[2]
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	(46)	[2]			(45)	[2]
Economic loss development after recoveries for R&W	(3)	[2]	2	[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	42	[2]			58	[2]
Economic loss development after recoveries for R&W	$ (17)	[2]	$ (11)	[2]

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

[2] Refer to Note 8, Financial Guaranty Contracts Accounted for as Credit Derivatives.

[3] Refer to Note 9, Consolidated Variable Interest Entities.