Derivative Instruments and Other Financial Instruments Used For Hedging - Gain or (Loss) Recognized in Income on Derivative Instruments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Trading Derivatives
Trading account activities	$ (10)	$ (3)
Trading derivatives
Trading Derivatives
Trading account activities	30	(24)	$ 169	$ (36)
Trading derivatives | Interest rate derivative contracts
Trading Derivatives
Trading account activities	17	(36)	130	(58)
Trading derivatives | Equity contracts
Trading Derivatives
Trading account activities	1	0	18	0
Trading derivatives | Foreign exchange derivative contracts
Trading Derivatives
Trading account activities	12	11	21	21
Trading derivatives | Commodity [Member]
Trading Derivatives
Trading account activities	$ 0	$ 1	$ 0	$ 1