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, 2015	Dec. 31, 2014	Dec. 31, 2013
Gain (Loss) on Derivative Instruments, Net, Pretax [Abstract]
Derivatives gains/(losses) recorded in income	$ 936	$ 2,399	$ 654
Interest rate
Gain (Loss) on Derivative Instruments, Net, Pretax [Abstract]
Derivatives gains/(losses) recorded in income	853	2,308	617
Credit
Gain (Loss) on Derivative Instruments, Net, Pretax [Abstract]
Derivatives gains/(losses) recorded in income	70	(58)	(142)
Foreign exchange
Gain (Loss) on Derivative Instruments, Net, Pretax [Abstract]
Derivatives gains/(losses) recorded in income	25	(7)	1
Commodity
Gain (Loss) on Derivative Instruments, Net, Pretax [Abstract]
Derivatives gains/(losses) recorded in income	$ (12)	$ 156	$ 178