Derivative instruments - Impact on Statements of Income, Risk Management Derivatives (Details) - Risk Management Activities - Not designated as hedges - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Gain (Loss) on Derivative Instruments, Net, Pretax [Abstract]
Derivatives gains/(losses) recorded in income	$ 767	$ 336	$ 845	$ 1,561
Interest rate
Gain (Loss) on Derivative Instruments, Net, Pretax [Abstract]
Derivatives gains/(losses) recorded in income	665	321	785	1,428
Credit
Gain (Loss) on Derivative Instruments, Net, Pretax [Abstract]
Derivatives gains/(losses) recorded in income	76	1	52	(40)
Foreign exchange
Gain (Loss) on Derivative Instruments, Net, Pretax [Abstract]
Derivatives gains/(losses) recorded in income	26	(2)	21	(5)
Commodity
Gain (Loss) on Derivative Instruments, Net, Pretax [Abstract]
Derivatives gains/(losses) recorded in income	$ 0	$ 16	$ (13)	$ 178