Derivative Instruments - Impact on Statements of Income, Risk Management Derivatives (Details) - Risk Management Activities - Not designated as hedges - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Gain (Loss) on Derivative Instruments, Net, Pretax [Abstract]
Derivatives gains/(losses) recorded in income	$ 175	$ 150	$ 872
Interest rate
Gain (Loss) on Derivative Instruments, Net, Pretax [Abstract]
Derivatives gains/(losses) recorded in income	79	331	1,174
Credit
Gain (Loss) on Derivative Instruments, Net, Pretax [Abstract]
Derivatives gains/(losses) recorded in income	(21)	(74)	(282)
Foreign exchange
Gain (Loss) on Derivative Instruments, Net, Pretax [Abstract]
Derivatives gains/(losses) recorded in income	$ 117	$ (107)	$ (20)