Financial Guaranty Contracts Accounted for as Credit Derivatives - Net Fair Value and Expected Losses of Credit Derivatives by Sector (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Credit Derivatives
Net fair value of credit derivatives	$ (895)	[1]	$ (1,693)
Expected Loss to be (Paid) Recovered	(58)	[2]	(184)	[2]
Pooled corporate obligations [Member]
Credit Derivatives
Net fair value of credit derivatives	(49)		(30)
Expected Loss to be (Paid) Recovered	(23)	[2]	(48)	[2]
RMBS [Member] | United States [Member]
Credit Derivatives
Net fair value of credit derivatives	(494)		(1,308)
Expected Loss to be (Paid) Recovered	(73)	[2]	(175)	[2]
CMBS [Member]
Credit Derivatives
Net fair value of credit derivatives	0		(2)
Expected Loss to be (Paid) Recovered	0	[2]	0	[2]
Other [Member]
Credit Derivatives
Net fair value of credit derivatives	(352)		(353)
Expected Loss to be (Paid) Recovered	38	[2]	39	[2]
Credit Risk Contract [Member]
Credit Derivatives
R&W Included in Credit Derivative Asset (Liability)	$ 86		$ 180

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

[2] Includes R&W benefit of $86 million as of December 31, 2014 and $180 million as of December 31, 2013.