Financial Guaranty Contracts Accounted for as Credit Derivatives - Effect of Changes in Credit Spread (Details) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2016		Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Credit Risk Derivatives, 100 Percent Widening in Spreads, Effect on Fair Value	[1]	$ (805)
Credit Risk Derivatives, 50 Percent Widening in Spreads, Effect on Fair Value	[1]	(601)
Credit Risk Derivatives, 25 Percent Widening in Spreads, Effect on Fair Value	[1]	(499)
Credit Risk Derivatives, 10 Percent Widening in Spreads, Effect on Fair Value	[1]	(437)
Base Scenario		(396)	[1]	$ (365)
Credit Risk Derivatives, 10 Percent Narrowing in Spreads, Effect on Fair Value	[1]	(358)
Credit Risk Derivatives, 25 Percent Narrowing in Spreads, Effect on Fair Value	[1]	(301)
Credit Risk Derivatives, 50 Percent Narrowing in Spreads, Effect on Fair Value	[1]	(206)
Credit Risk Derivatives, 100 Percent Widening in Spreads, Effect on Unrealized Gain (Loss)	[1]	(409)
Credit Risk Derivatives, 50 Percent Widening in Spreads, Effect on Unrealized Gain (Loss)	[1]	(205)
Credit Risk Derivatives, 25 Percent Widening in Spreads, Effect on Unrealized Gain (Loss)	[1]	(103)
Credit Risk Derivatives, 10 Percent Widening in Spreads, Effect on Unrealized Gain (Loss)	[1]	(41)
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]	38
Credit Risk Derivatives, 25 Percent Narrowing in Spreads, Effect on Unrealized Gain (Loss)	[1]	95
Credit Risk Derivatives, 50 Percent Narrowing in Spreads, Effect on Unrealized Gain (Loss)	[1]	$ 190

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