Other Noninterest Expense - Summary of Other Noninterest Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Other Income and Expenses [Abstract]
Lending and other client related processing costs	$ 8	$ 7	$ 15	$ 16
Correspondent bank fees	5	4	9	8
Investment banking activities	3	8	9	11
Trade order execution costs	3	2	6	5
Data processing services	5	3	10	7
Telephone	2	2	4	4
Dues and publications	1	1	3	2
Postage and supplies	1	1	1	1
Other	17	11	33	26
Total other noninterest expense	$ 45	$ 39	$ 90	$ 80