Derivative Instruments - Impact on Statements of Income, Risk Management Derivatives (Details) - Risk Management Activities - Not designated as hedges - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Gain (Loss) on Derivative Instruments, Net, Pretax [Abstract]
Derivatives gains/(losses) recorded in income	$ 580	$ 105	$ 912	$ (142)
Interest rate
Gain (Loss) on Derivative Instruments, Net, Pretax [Abstract]
Derivatives gains/(losses) recorded in income	657	(25)	949	(235)
Credit
Gain (Loss) on Derivative Instruments, Net, Pretax [Abstract]
Derivatives gains/(losses) recorded in income	(2)	(3)	(12)	(10)
Foreign exchange
Gain (Loss) on Derivative Instruments, Net, Pretax [Abstract]
Derivatives gains/(losses) recorded in income	$ (75)	$ 133	$ (25)	$ 103