Financial Guaranty Contracts Accounted for as Credit Derivatives - Net Fair Value and Expected Losses In Excess of Premiums of Credit Derivatives by Sector (Details) (USD $)	3 Months Ended
	Mar. 31, 2014		Dec. 31, 2013		Mar. 31, 2013	Mar. 31, 2014 5 year spread AGC	Dec. 31, 2013 5 year spread AGC	Dec. 31, 2012 5 year spread AGC	Mar. 31, 2014 5 year spread AGM	Dec. 31, 2013 5 year spread AGM	Dec. 31, 2012 5 year spread AGM	Mar. 31, 2014 1 year spread AGC	Dec. 31, 2013 1 year spread AGC	Dec. 31, 2012 1 year spread AGC	Mar. 31, 2014 1 year spread AGM	Dec. 31, 2013 1 year spread AGM	Dec. 31, 2012 1 year spread AGM	Mar. 31, 2014 Pooled corporate obligations		Dec. 31, 2013 Pooled corporate obligations		Mar. 31, 2014 U.S. RMBS		Dec. 31, 2013 U.S. RMBS		Mar. 31, 2014 CMBS		Dec. 31, 2013 CMBS		Mar. 31, 2014 Other		Dec. 31, 2013 Other
Components of Credit Derivative Assets (Liabilities)
Quoted price of CDS contract (as a percent)						2.91%	4.60%	6.78%	3.05%	5.25%	5.36%	0.55%	1.85%	2.70%	0.70%	2.20%	2.57%
Gain from tightening of spreads	$ 347,000,000
Fair value of credit derivatives before effect of AGC and AGM credit spreads
Fair value of credit derivatives before effect of AGC and AGM credit spreads	(3,095,000,000)		(3,442,000,000)
Plus: Effect of AGC and AGM credit spreads	1,172,000,000		1,749,000,000
Net fair value of credit derivatives	(1,923,000,000)		(1,693,000,000)															(89,000,000)		(30,000,000)		(1,448,000,000)		(1,308,000,000)		(2,000,000)		(2,000,000)		(384,000,000)		(353,000,000)
Present Value of Expected Claim (Payments) Recoveries In Excess of Premiums	(134,000,000)	[1]	(139,000,000)	[1]														(20,000,000)	[1]	(35,000,000)	[1]	(154,000,000)	[1]	(147,000,000)	[1]	0	[1]	0	[1]	40,000,000	[1]	43,000,000	[1]
Present Value of Future Installment Fees Receivable	39,000,000		45,000,000
R and W Included in Credit Derivative Asset (Liability)	175,000,000		180,000,000
Other credit derivative disclosures
Par insured that could be terminated if ratings were downgraded	1,600,000,000
Amount of par subject to collateral posting	9,800,000,000
Cap on collateral requirement at current ratings levels	9,500,000,000
Amount of par subject to collateral for which the amount of collateral is capped	665,000,000
Credit Derivative, Notional Amount Subject to Collateral based in MTM valuation	341,000,000				347,000,000
Collateral agreed to be posted	669,000,000				677,000,000
Credit Derivative, Collateral Posted, based in MTM valuation	$ 54,000,000				$ 62,000,000

[1] Represents the expected claim payments (recoveries) in excess of the present value of future installment fees to be received of $39 million as of March 31, 2014 and $45 million as of December 31, 2013. Includes R&W benefit of $175 million as of March 31, 2014 and $180 million as of December 31, 2013.