Financial Guaranty Contracts Accounted for as Credit Derivatives - Effect of Changes in Credit Spread (Details) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2015		Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Credit Risk Derivatives, 100 Percent Widening in Spreads, Effect on Fair Value	[1]	$ (1,723)
Credit Risk Derivatives, 50 Percent Widening in Spreads, Effect on Fair Value	[1]	(1,285)
Credit Risk Derivatives, 25 Percent Widening in Spreads, Effect on Fair Value	[1]	(1,067)
Credit Risk Derivatives, 10 Percent Widening in Spreads, Effect on Fair Value	[1]	(935)
Net fair value of credit derivatives	[2]	(847)	[1]	$ (895)
Credit Risk Derivatives, 10 Percent Narrowing in Spreads, Effect on Fair Value	[1]	(765)
Credit Risk Derivatives, 25 Percent Narrowing in Spreads, Effect on Fair Value	[1]	(643)
Credit Risk Derivatives, 50 Percent Narrowing in Spreads, Effect on Fair Value	[1]	(441)
Credit Risk Derivatives, 100 Percent Widening in Spreads, Effect on Unrealized Gain (Loss)	[1]	(876)
Credit Risk Derivatives, 50 Percent Widening in Spreads, Effect on Unrealized Gain (Loss)	[1]	(438)
Credit Risk Derivatives, 25 Percent Widening in Spreads, Effect on Unrealized Gain (Loss)	[1]	(220)
Credit Risk Derivatives, 10 Percent Widening in Spreads, Effect on Unrealized Gain (Loss)	[1]	(88)
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]	82
Credit Risk Derivatives, 25 Percent Narrowing in Spreads, Effect on Unrealized Gain (Loss)	[1]	204
Credit Risk Derivatives, 50 Percent Narrowing in Spreads, Effect on Unrealized Gain (Loss)	[1]	$ 406

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

[2] September 30, 2015 amount includes $174 million of net fair value loss of credit derivatives acquired from Radian Asset.