Financial Guaranty Contracts Accounted for as Credit Derivatives (Details 4) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012	Dec. 31, 2012
Credit Derivatives
Net unrealized gains (losses)	$ (610)		$ (634)
Net fair value of credit derivatives	(2,393)			(1,793)
Present Value of Expected Claim Payments Recoveries	(286)	[1]		(282)	[1]
Present Value of Future Installment Fees Receivable	42			43
R and W Included in Credit Derivative Asset (Liability)	226			237
Pooled Corporate Obligations [Member]
Credit Derivatives
Net unrealized gains (losses)	(105)		5
Net fair value of credit derivatives	(101)			6
Present Value of Expected Claim Payments Recoveries	(13)	[1]		(16)	[1]
CLOs/CBOs
Credit Derivatives
Net unrealized gains (losses)	(54)		7
Net fair value of credit derivatives	(52)			3
Present Value of Expected Claim Payments Recoveries	0	[1]		0	[1]
Synthetic investment grade pooled corporate
Credit Derivatives
Net unrealized gains (losses)	2		2
Net fair value of credit derivatives	(3)			(5)
Present Value of Expected Claim Payments Recoveries	0	[1]		0	[1]
Synthetic high yield pooled corporate
Credit Derivatives
Net unrealized gains (losses)	(1)		11
Net fair value of credit derivatives	2			3
Present Value of Expected Claim Payments Recoveries	0	[1]		0	[1]
Trust Preferred Securities Collateralized Debt Obligations
Credit Derivatives
Net unrealized gains (losses)	(39)		(14)
Net fair value of credit derivatives	(37)			3
Present Value of Expected Claim Payments Recoveries	(13)	[1]		(16)	[1]
Market value collateralized debt obligations of corporate obligations
Credit Derivatives
Net unrealized gains (losses)	(13)		(1)
Net fair value of credit derivatives	(11)			2
Present Value of Expected Claim Payments Recoveries	0	[1]		0	[1]
U.S. RMBS
Credit Derivatives
Net unrealized gains (losses)	(457)		(629)
Net fair value of credit derivatives	(1,693)			(1,237)
Present Value of Expected Claim Payments Recoveries	(182)	[1]		(181)	[1]
Option ARM and Alt-A first lien
Credit Derivatives
Net unrealized gains (losses)	(295)		(518)
Net fair value of credit derivatives	(1,394)			(1,076)
Present Value of Expected Claim Payments Recoveries	(109)	[1]		(121)	[1]
Subprime first lien
Credit Derivatives
Net unrealized gains (losses)	(79)		(26)
Net fair value of credit derivatives	(109)			(52)
Present Value of Expected Claim Payments Recoveries	(77)	[1]		(70)	[1]
Prime first lien
Credit Derivatives
Net unrealized gains (losses)	(83)		(86)
Net fair value of credit derivatives	(179)			(99)
Present Value of Expected Claim Payments Recoveries	(6)	[1]		0	[1]
Closed end second lien and HELOCs
Credit Derivatives
Net unrealized gains (losses)	0		1
Net fair value of credit derivatives	(11)			(10)
Present Value of Expected Claim Payments Recoveries	10	[1]		10	[1]
CMBS
Credit Derivatives
Net unrealized gains (losses)	(3)		0
Net fair value of credit derivatives	(5)			(2)
Present Value of Expected Claim Payments Recoveries	0	[1]		0	[1]
Other
Credit Derivatives
Net unrealized gains (losses)	(45)		(10)
Net fair value of credit derivatives	(594)			(560)
Present Value of Expected Claim Payments Recoveries	(91)	[1]		(85)	[1]
Other | Guaranteed Interest Rate Swaps
Credit Derivatives
Net unrealized gains (losses)	$ 20

[1] Represents amount in excess of the present value of future installment fees to be received of $42 million as of March 31, 2013 and $43 million as of December 31, 2012. Includes R&W benefit of $226 million as of March 31, 2013 and $237 million as of December 31, 2012.