Financial Guaranty Contracts Accounted for as Credit Derivatives - Net Fair Value and Expected Losses of Credit Derivatives by Sector (Details) - USD ($) $ in Millions	Mar. 31, 2016		Dec. 31, 2015
Credit Derivatives
Net fair value of credit derivatives	$ (434)	[1]	$ (365)
Expected Loss to be (Paid) Recovered	(9)		(16)
Pooled corporate obligations [Member]
Credit Derivatives
Net fair value of credit derivatives	(131)		(82)
Expected Loss to be (Paid) Recovered	(4)		(5)
RMBS [Member] | United States [Member]
Credit Derivatives
Net fair value of credit derivatives	(113)		(98)
Expected Loss to be (Paid) Recovered	(33)		(38)
CMBS [Member]
Credit Derivatives
Net fair value of credit derivatives	0		0
Expected Loss to be (Paid) Recovered	0		0
Other [Member]
Credit Derivatives
Net fair value of credit derivatives	(190)		(185)
Expected Loss to be (Paid) Recovered	$ 28		$ 27

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