Contracts Accounted for as Credit Derivatives - Net Fair Value and Expected Losses of Credit Derivatives by Sector (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Fair Value of Credit Derivative Asset (Liability), net	$ (302)	$ (389)
Expected Loss on Credit Derivative to Be Paid (Recovered), Including Representation and Warranty Liability (Benefit)	$ 6	$ (10)