Noninterest Income - Foreign Exchange Fees (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 306	$ 285	$ 633	$ 506
Revenue not from contract with customer	455	84	872	164
Foreign exchange fees	67	36	124	84
Spot contract commissions
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	60	33	115	74
Forward contract commissions
Disaggregation of Revenue [Line Items]
Revenue not from contract with customer	6	3	8	10
Option premium fees
Disaggregation of Revenue [Line Items]
Revenue not from contract with customer	$ 1	$ 0	$ 1	$ 0