Derivative Financial Instruments - Impact of Derivatives on Consolidated Statement of Income (Details) - Derivatives not designated as hedging instruments - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	$ 271	$ 46
Foreign exchange contracts | Foreign exchange trading services
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	333	160
Foreign exchange contracts | Interest expense
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	2	(39)
Interest rate contracts | Foreign exchange trading services
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	3	(1)
Other derivative contracts | Compensation and employee benefits
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	$ (67)	$ (74)