Financial Guaranty Contracts Accounted for as Credit Derivatives - CDS Spread and Components of Credit Derivative Assets (Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
Credit Derivatives
Fair value of credit derivatives before effect of AGC and AGM credit spreads	(2,029)		(3,442)
Plus: Effect of AGC and AGM credit spreads	1,134		1,749
Net fair value of credit derivatives	(895)	[1]	(1,693)
Credit Risk Contract, 5 Year Spread [Member] | AGC [Member]
Credit Derivatives
Quoted price of CDS contract (as a percent)	3.23%		4.60%	6.78%
Credit Risk Contract, 5 Year Spread [Member] | AGM [Member]
Credit Derivatives
Quoted price of CDS contract (as a percent)	3.25%		5.25%	5.36%
Credit Risk Contract, 1 Year Spread [Member] | AGC [Member]
Credit Derivatives
Quoted price of CDS contract (as a percent)	0.80%		1.85%	2.70%
Credit Risk Contract, 1 Year Spread [Member] | AGM [Member]
Credit Derivatives
Quoted price of CDS contract (as a percent)	0.85%		2.20%	2.57%

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