Financial Guaranty Contracts Accounted for as Credit Derivatives - CDS Spread and Components of Credit Derivative Assets (Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Credit Derivatives
Fair value of credit derivatives before effect of AGC and AGM credit spreads	(1,820)		(2,029)
Plus: Effect of AGC and AGM credit spreads	1,038		1,134
Net fair value of credit derivatives	(782)	[1]	(895)
Credit Risk Contract, 5 Year Spread [Member] | AGC [Member]
Credit Derivatives
Quoted price of CDS contract (as a percent)	3.17%		3.23%	2.91%	4.60%
Credit Risk Contract, 5 Year Spread [Member] | AGM [Member]
Credit Derivatives
Quoted price of CDS contract (as a percent)	3.41%		3.25%	3.05%	5.25%
Credit Risk Contract, 1 Year Spread [Member] | AGC [Member]
Credit Derivatives
Quoted price of CDS contract (as a percent)	0.60%		0.80%	0.55%	1.85%
Credit Risk Contract, 1 Year Spread [Member] | AGM [Member]
Credit Derivatives
Quoted price of CDS contract (as a percent)	0.80%		0.85%	0.70%	2.20%

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