Noninterest Income - Client Investment 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
Sweep money market fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	12	18	31	61
Asset management fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	7	12	22	33
Repurchase agreement fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	2	2	13
Client investment fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 20	$ 32	$ 55	$ 107