Financial Guaranty Contracts Accounted for as Credit Derivatives - CDS Spread and Components of Credit Derivative Assets (Liabilities) (Details) - USD ($) $ in Millions		Sep. 30, 2015		Jun. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013
Credit Derivatives
Fair value of credit derivatives before effect of AGC and AGM credit spreads		$ (1,973)			$ (2,029)
Plus: Effect of AGC and AGM credit spreads		1,126			1,134
Net fair value of credit derivatives	[2]	$ (847)	[1]		$ (895)
Credit Risk Contract, 5 Year Spread [Member] | AGC [Member]
Credit Derivatives
Quoted price of CDS contract (as a percent)		3.31%		3.90%	3.23%	3.45%	3.27%	4.60%
Credit Risk Contract, 5 Year Spread [Member] | AGM [Member]
Credit Derivatives
Quoted price of CDS contract (as a percent)		3.37%		4.10%	3.25%	3.44%	3.46%	5.25%
Credit Risk Contract, 1 Year Spread [Member] | AGC [Member]
Credit Derivatives
Quoted price of CDS contract (as a percent)		1.12%		1.20%	0.80%	1.25%	0.85%	1.85%
Credit Risk Contract, 1 Year Spread [Member] | AGM [Member]
Credit Derivatives
Quoted price of CDS contract (as a percent)		1.04%		1.25%	0.85%	1.20%	1.15%	2.20%
Radian [Member]
Credit Derivatives
Net fair value of credit derivatives		$ 174

[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.