Financial Guaranty Contracts Accounted for as Credit Derivatives - Effect of Changes in Credit Spread (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016		Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Credit Risk Derivatives, 100 Percent Widening in Spreads, Effect on Fair Value	[1]	$ (883)
Credit Risk Derivatives, 50 Percent Widening in Spreads, Effect on Fair Value	[1]	(658)
Credit Risk Derivatives, 25 Percent Widening in Spreads, Effect on Fair Value	[1]	(547)
Credit Risk Derivatives, 10 Percent Widening in Spreads, Effect on Fair Value	[1]	(479)
Net fair value of credit derivatives		(434)	[1]	$ (365)
Credit Risk Derivatives, 10 Percent Narrowing in Spreads, Effect on Fair Value	[1]	(392)
Credit Risk Derivatives, 25 Percent Narrowing in Spreads, Effect on Fair Value	[1]	(329)
Credit Risk Derivatives, 50 Percent Narrowing in Spreads, Effect on Fair Value	[1]	(226)
Credit Risk Derivatives, 100 Percent Widening in Spreads, Effect on Unrealized Gain (Loss)	[1]	(449)
Credit Risk Derivatives, 50 Percent Widening in Spreads, Effect on Unrealized Gain (Loss)	[1]	(224)
Credit Risk Derivatives, 25 Percent Widening in Spreads, Effect on Unrealized Gain (Loss)	[1]	(113)
Credit Risk Derivatives, 10 Percent Widening in Spreads, Effect on Unrealized Gain (Loss)	[1]	(45)
Credit Risk Derivatives, Base Scenario, Effect on Unrealized Gain (Loss)	[1]	0
Credit Risk Derivatives, 10 Percent Narrowing in Spreads, Effect on Unrealized Gain (Loss)	[1]	42
Credit Risk Derivatives, 25 Percent Narrowing in Spreads, Effect on Unrealized Gain (Loss)	[1]	105
Credit Risk Derivatives, 50 Percent Narrowing in Spreads, Effect on Unrealized Gain (Loss)	[1]	$ 208

[1] Includes the effects of spreads on both the underlying asset classes and the Company’s own credit spread.