Financial Guaranty Contracts Accounted for as Credit Derivatives - Net Fair Value and Expected Losses of Credit Derivatives by Sector (Details) (USD $)	9 Months Ended																																																						0 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 5 year spread AGC	Jun. 30, 2014 5 year spread AGC	Dec. 31, 2013 5 year spread AGC	Sep. 30, 2013 5 year spread AGC	Jun. 30, 2013 5 year spread AGC	Dec. 31, 2012 5 year spread AGC	Sep. 30, 2014 5 year spread AGM	Jun. 30, 2014 5 year spread AGM	Dec. 31, 2013 5 year spread AGM	Sep. 30, 2013 5 year spread AGM	Jun. 30, 2013 5 year spread AGM	Dec. 31, 2012 5 year spread AGM	Sep. 30, 2014 1 year spread AGC	Jun. 30, 2014 1 year spread AGC	Dec. 31, 2013 1 year spread AGC	Sep. 30, 2013 1 year spread AGC	Jun. 30, 2013 1 year spread AGC	Dec. 31, 2012 1 year spread AGC	Sep. 30, 2014 1 year spread AGM	Jun. 30, 2014 1 year spread AGM	Dec. 31, 2013 1 year spread AGM	Sep. 30, 2013 1 year spread AGM	Jun. 30, 2013 1 year spread AGM	Dec. 31, 2012 1 year spread AGM	Sep. 30, 2014 Pooled corporate obligations	Dec. 31, 2013 Pooled corporate obligations	Sep. 30, 2014 U.S. RMBS	Dec. 31, 2013 U.S. RMBS	Sep. 30, 2014 CMBS	Dec. 31, 2013 CMBS	Sep. 30, 2014 Other	Dec. 31, 2013 Other	Sep. 30, 2014 Credit derivatives		Dec. 31, 2013 Credit derivatives		Sep. 30, 2014 Credit derivatives Pooled corporate obligations		Dec. 31, 2013 Credit derivatives Pooled corporate obligations		Sep. 30, 2014 Credit derivatives U.S. RMBS		Dec. 31, 2013 Credit derivatives U.S. RMBS		Sep. 30, 2014 Credit derivatives CMBS		Dec. 31, 2013 Credit derivatives CMBS		Sep. 30, 2014 Credit derivatives Other		Dec. 31, 2013 Credit derivatives Other		Oct. 07, 2014 Subsequent event	Oct. 07, 2014 Credit derivatives Subsequent event Transaction
Components of Credit Derivative Assets (Liabilities)
Fair value losses that will reverse to gains upon termination of transactions																																																							$ 372,000,000
Quoted price of CDS contract (as a percent)			3.45%	3.27%	4.60%	4.65%	3.43%	6.78%	3.44%	3.46%	5.25%	5.02%	3.65%	5.36%	1.25%	0.85%	1.85%	1.85%	0.57%	2.70%	1.20%	1.15%	2.20%	2.15%	0.72%	2.57%
Gain from tightening of spreads	687,000,000
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	(2,755,000,000)	(3,442,000,000)
Plus: Effect of AGC and AGM credit spreads	1,187,000,000	1,749,000,000
Net fair value of credit derivatives	(1,568,000,000)	(1,693,000,000)																									(22,000,000)	(30,000,000)	(1,192,000,000)	(1,308,000,000)	0	(2,000,000)	(354,000,000)	(353,000,000)
Expected Loss to be (Paid) Recovered	(937,000,000)	(985,000,000)																											(381,000,000)	(493,000,000)					(83,000,000)	[1]	(184,000,000)	[1]	(26,000,000)	[1]	(48,000,000)	[1]	(97,000,000)	[1]	(175,000,000)	[1]	0	[1]	0	[1]	40,000,000	[1]	39,000,000	[1]
R and W Included in Credit Derivative Asset (Liability)	99,000,000	180,000,000
Number of transactions terminated																																																								3
Other credit derivative disclosures
Amount of par subject to collateral posting	7,200,000,000
Cap on collateral requirement at current ratings levels	6,900,000,000
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	337,000,000	347,000,000
Collateral agreed to be posted	434,000,000	677,000,000
Credit Derivative, Collateral Posted, based in MTM valuation	$ 40,000,000	$ 62,000,000

[1] Includes R&W benefit of $99 million as of September 30, 2014 and $180 million as of December 31, 2013.