Contracts Accounted for as Credit Derivatives - Credit Derivatives Subordination and Ratings (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	$ 6,207	$ 16,997
Pooled corporate obligations [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	878	10,425
Pooled corporate obligations [Member] | Collateralized Loan Obligations and Collateral Bond Obligations [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	0	2,022
Pooled corporate obligations [Member] | Synthetic investment grade pooled corporate [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	0	7,224
Pooled corporate obligations [Member] | TruPS CDOs [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	878	1,179
Residential Mortgage-Backed Securities (RMBS) [Member] | United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	916	1,142
Pooled infrastructure [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	1,561	1,513
Infrastructure finance [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	572	1,021
Other [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	$ 2,280	$ 2,896