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	Mar. 31, 2015		Dec. 31, 2014
Credit Derivatives
Net fair value of credit derivatives	$ (782)	[1]	$ (895)
Expected Loss to be (Paid) Recovered	(42)	[2]	(58)	[2]
Pooled corporate obligations [Member]
Credit Derivatives
Net fair value of credit derivatives	(22)		(49)
Expected Loss to be (Paid) Recovered	(13)	[2]	(23)	[2]
RMBS [Member] | United States [Member]
Credit Derivatives
Net fair value of credit derivatives	(419)		(494)
Expected Loss to be (Paid) Recovered	(66)	[2]	(73)	[2]
CMBS [Member]
Credit Derivatives
Net fair value of credit derivatives	0		0
Expected Loss to be (Paid) Recovered	0	[2]	0	[2]
Other [Member]
Credit Derivatives
Net fair value of credit derivatives	(341)		(352)
Expected Loss to be (Paid) Recovered	37	[2]	38	[2]
Credit Risk Contract [Member]
Credit Derivatives
R&W Included in Credit Derivative Asset (Liability)	$ 75		$ 86

[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 $75 million as of March 31, 2015 and $86 million as of December 31, 2014.