Noninterest Income - Foreign Exchange Fees (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 315	$ 247	$ 948	$ 757
Revenue not from contract with customer	357	300	1,229	461
Foreign exchange fees	65	44	189	128
Spot contract commissions
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	60	39	175	113
Forward contract commissions
Disaggregation of Revenue [Line Items]
Revenue not from contract with customer	5	5	13	14
Option premium fees
Disaggregation of Revenue [Line Items]
Revenue not from contract with customer	$ 0	$ 0	$ 1	$ 1