Noninterest Income - Client Investment 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
Sweep money market fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	7	19	18	42
Asset management fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8	12	16	21
Repurchase agreement fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	1	1	12
Client investment fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 15	$ 32	$ 35	$ 75