Derivative Financial Instruments - Impact of Derivatives on Consolidated Statement of Income (Details) - Derivatives not designated as hedging instruments - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	$ 116	$ 199	$ 361	$ 624
Foreign exchange contracts | Trading services
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	152	161	485	477
Foreign exchange contracts | Processing fees and other revenue
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	(9)	(3)	(11)	(13)
Interest-rate contracts | Trading services
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	(2)	(1)	7	(6)
Interest-rate contracts | Processing fees and other revenue
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	0	0	0	1
Credit derivative contracts | Trading services
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	0	0	0	(1)
Other derivative contracts | Trading services
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	0	1	0	(2)
Other derivative contracts | Compensation and employee benefits
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	$ (25)	$ 41	$ (120)	$ 168