Financial Guaranty Contracts Accounted for as Credit Derivatives - CDS Spread and Components of Credit Derivative Assets (Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2016		Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Credit Derivatives
Fair value of credit derivatives before effect of AGC and AGM credit spreads	$ (1,509)		$ (1,448)
Plus: Effect of AGC and AGM credit spreads	1,075		1,083
Net fair value of credit derivatives	$ (434)	[1]	$ (365)
Credit Risk Contract, 5 Year Spread [Member] | AGC [Member]
Credit Derivatives
Quoted price of CDS contract (as a percent)	3.07%		3.76%	3.17%	3.23%
Credit Risk Contract, 5 Year Spread [Member] | AGM [Member]
Credit Derivatives
Quoted price of CDS contract (as a percent)	3.09%		3.66%	3.41%	3.25%
Credit Risk Contract, 1 Year Spread [Member] | AGC [Member]
Credit Derivatives
Quoted price of CDS contract (as a percent)	1.05%		1.39%	0.60%	0.80%
Credit Risk Contract, 1 Year Spread [Member] | AGM [Member]
Credit Derivatives
Quoted price of CDS contract (as a percent)	1.02%		1.31%	0.80%	0.85%

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