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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	$ 167	$ 145	$ 513	$ 603
Foreign exchange contracts | Foreign exchange trading services
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	186	164	617	712
Foreign exchange contracts | Interest expense
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	16	20	53	39
Interest rate contracts | Foreign exchange trading services
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	0	0	1	3
Other derivative contracts | Compensation and employee benefits
Derivative [Line Items]
Amount of gain (loss) on derivative recognized in income	$ (35)	$ (39)	$ (158)	$ (151)