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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	$ 76	$ 133	$ 173	$ 387
Foreign exchange contracts | Foreign exchange trading services
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	160	170	476	549
Foreign exchange contracts | Interest Expense
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	(37)	(3)	(135)	(18)
Interest rate contracts | Foreign exchange trading services
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	(1)	(2)	(2)	(6)
Interest rate contracts | Processing fees and other revenue
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	0	(1)	0	(1)
Other derivative contracts | Foreign exchange trading services
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	0	3	0	3
Other derivative contracts | Compensation and employee benefits
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	$ (46)	$ (34)	$ (166)	$ (140)