Expected Loss to be Paid - Net Expected Loss to be Paid After Net Expected Recoveries for Breaches of R&W Rollforward (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	$ 1,169	[1]	$ 982	[1]
Economic loss development after recoveries for R&W	(3)		12
(Paid) Recovered Losses After Recoveries for R&W	(12)	[2]	(10)	[2]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	1,154	[1]	984	[1]
Period after the end of the reporting period within which the ceded paid losses are typically settled (in days)	45 days
Loss and LAE Reserve paid	4		6
Expected LAE to be paid	13				16
Subtotal [Member]
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	1,173	[1]	985	[1]
Economic loss development after recoveries for R&W	(2)		13
(Paid) Recovered Losses After Recoveries for R&W	(18)	[2]	(10)	[2]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	1,153	[1]	988	[1]
Public Finance [Member]
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	348	[1]	321	[1]
Economic loss development after recoveries for R&W	6		23
(Paid) Recovered Losses After Recoveries for R&W	(2)	[2]	(6)	[2]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	352	[1]	338	[1]
Public Finance [Member] | United States [Member]
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	303	[1]	264	[1]
Economic loss development after recoveries for R&W	9		23
(Paid) Recovered Losses After Recoveries for R&W	(2)	[2]	(6)	[2]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	310	[1]	281	[1]
Public Finance [Member] | Non United States [Member]
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	45	[1]	57	[1]
Economic loss development after recoveries for R&W	(3)		0
(Paid) Recovered Losses After Recoveries for R&W	0	[2]	0	[2]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	42	[1]	57	[1]
RMBS [Member] | United States [Member]
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	584	[1]	493	[1]
Economic loss development after recoveries for R&W	4		(10)
(Paid) Recovered Losses After Recoveries for R&W	(18)	[2]	(3)	[2]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	570	[1]	480	[1]
RMBS [Member] | First Lien [Member] | United States [Member]
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	595	[1]	620	[1]
Economic loss development after recoveries for R&W	(2)		(17)
(Paid) Recovered Losses After Recoveries for R&W	(24)	[2]	(10)	[2]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	569	[1]	593	[1]
RMBS [Member] | First Lien [Member] | Prime [Member] | United States [Member]
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	4	[1]	21	[1]
Economic loss development after recoveries for R&W	0		(3)
(Paid) Recovered Losses After Recoveries for R&W	(1)	[2]	0	[2]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	3	[1]	18	[1]
RMBS [Member] | First Lien [Member] | Alt-A [Member] | United States [Member]
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	304	[1]	304	[1]
Economic loss development after recoveries for R&W	(5)		8
(Paid) Recovered Losses After Recoveries for R&W	(10)	[2]	(4)	[2]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	289	[1]	308	[1]
RMBS [Member] | First Lien [Member] | Option ARM [Member] | United States [Member]
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	(16)	[1]	(9)	[1]
Economic loss development after recoveries for R&W	4		(15)
(Paid) Recovered Losses After Recoveries for R&W	(4)	[2]	(4)	[2]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	(16)	[1]	(28)	[1]
RMBS [Member] | First Lien [Member] | Subprime [Member] | United States [Member]
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	303	[1]	304	[1]
Economic loss development after recoveries for R&W	(1)		(7)
(Paid) Recovered Losses After Recoveries for R&W	(9)	[2]	(2)	[2]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	293	[1]	295	[1]
RMBS [Member] | Second Lien [Member] | United States [Member]
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	(11)	[1]	(127)	[1]
Economic loss development after recoveries for R&W	6		7
(Paid) Recovered Losses After Recoveries for R&W	6	[2]	7	[2]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	1	[1]	(113)	[1]
RMBS [Member] | Second Lien [Member] | Closed-end [Member] | United States [Member]
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	8	[1]	(11)	[1]
Economic loss development after recoveries for R&W	1		5
(Paid) Recovered Losses After Recoveries for R&W	2	[2]	2	[2]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	11	[1]	(4)	[1]
RMBS [Member] | Second Lien [Member] | HELOCs [Member] | United States [Member]
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	(19)	[1]	(116)	[1]
Economic loss development after recoveries for R&W	5		2
(Paid) Recovered Losses After Recoveries for R&W	4	[2]	5	[2]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	(10)	[1]	(109)	[1]
Triple-X Life Insurance Transaction [Member]
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	161	[1]	75	[1]
Economic loss development after recoveries for R&W	5		13
(Paid) Recovered Losses After Recoveries for R&W	(1)	[2]	(1)	[2]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	165	[1]	87	[1]
Trust Preferred Securities (TruPS) [Member]
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	23	[1]	51	[1]
Economic loss development after recoveries for R&W	(9)		(19)	[3]
(Paid) Recovered Losses After Recoveries for R&W	0	[2]	0	[2]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	14	[1]	32	[1]
Other structured finance [Member]
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	57	[1]	45	[1]
Economic loss development after recoveries for R&W	(8)		6
(Paid) Recovered Losses After Recoveries for R&W	3	[2]	0	[2]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	52	[1]	51	[1]
Structured Finance [Member]
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	825	[1]	664	[1]
Economic loss development after recoveries for R&W	(8)		(10)
(Paid) Recovered Losses After Recoveries for R&W	(16)	[2]	(4)	[2]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	801	[1]	650	[1]
Other Insurance Product Line [Member]
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	(4)	[1]	(3)	[1]
Economic loss development after recoveries for R&W	(1)		(1)
(Paid) Recovered Losses After Recoveries for R&W	6	[2]	0	[2]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	$ 1	[1]	$ (4)	[1]

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

[2] Net of ceded paid losses, whether or not such amounts have been settled with reinsurers. Ceded paid losses are typically settled 45 days after the end of the reporting period. Such amounts are recorded in reinsurance recoverable on paid losses included in other assets.

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