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	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
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	$ 982		$ 677
Economic loss development after recoveries for R&W	(30)		56
(Paid) Recovered Losses After Recoveries for R&W	217	[1]	249	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	1,169		982
Period after the end of the reporting period within which the ceded paid losses are typically settled (in days)	45 days
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	493		282
Economic loss development after recoveries for R&W	(268)		(156)
(Paid) Recovered Losses After Recoveries for R&W	359	[1]	367	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	584		493
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	620		432
Economic loss development after recoveries for R&W	(226)		(71)
(Paid) Recovered Losses After Recoveries for R&W	201	[1]	259	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	595		620
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	21		6
Economic loss development after recoveries for R&W	(16)		16
(Paid) Recovered Losses After Recoveries for R&W	(1)	[1]	(1)	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	4		21
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		315
Economic loss development after recoveries for R&W	(144)		(81)
(Paid) Recovered Losses After Recoveries for R&W	144	[1]	70	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	304		304
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	(9)		(131)
Economic loss development after recoveries for R&W	(59)		(98)
(Paid) Recovered Losses After Recoveries for R&W	52	[1]	220	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	(16)		(9)
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	304		242
Economic loss development after recoveries for R&W	(7)		92
(Paid) Recovered Losses After Recoveries for R&W	6	[1]	(30)	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	303		304
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	(127)		(150)
Economic loss development after recoveries for R&W	(42)		(85)
(Paid) Recovered Losses After Recoveries for R&W	158	[1]	108	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	(11)		(127)
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	(11)		(39)
Economic loss development after recoveries for R&W	3		6
(Paid) Recovered Losses After Recoveries for R&W	16	[1]	22	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	8		(11)
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	(116)		(111)
Economic loss development after recoveries for R&W	(45)		(91)
(Paid) Recovered Losses After Recoveries for R&W	142	[1]	86	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	(19)		(116)
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	51		27
Economic loss development after recoveries for R&W	(28)		7
(Paid) Recovered Losses After Recoveries for R&W	0	[1]	17	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	23		51
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	120		312
Economic loss development after recoveries for R&W	96		(41)
(Paid) Recovered Losses After Recoveries for R&W	2	[1]	(151)	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	218		120
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	264		7
Economic loss development after recoveries for R&W	183		239
(Paid) Recovered Losses After Recoveries for R&W	(144)	[1]	18	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	303		264
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	57		52
Economic loss development after recoveries for R&W	(12)		17
(Paid) Recovered Losses After Recoveries for R&W	0	[1]	(12)	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	45		57
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	(3)		(3)
Economic loss development after recoveries for R&W	(1)		(10)
(Paid) Recovered Losses After Recoveries for R&W	0	[1]	10	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	$ (4)		$ (3)

[1] Net of ceded paid losses, whether or not such amounts have been settled with reinsurers. Ceded paid losses and recoveries 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.