Business Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Fixed income	$ 406	$ 423	$ 279
Deposit transactions and cash management	175	148	132
Mortgage banking and title income	154	129	10
Brokerage, management fees and commissions	88	66	55
Card and digital banking fees	78	60	49
Trust services and investment management	51	39	30
Other service charges and fees	44	26	21
Securities gains (losses), net	13	(6)	0
Purchase accounting gain	(1)	533	0
Other income (loss)	68	74	78
Total noninterest income	1,076	1,492	654
Underwriting, Portfolio Advisory, and Other Noninterest Income
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	44	39	34
Regional Banking
Disaggregation of Revenue [Line Items]
Fixed income	0	1	0
Deposit transactions and cash management	157	131	114
Mortgage banking and title income	0	0	0
Brokerage, management fees and commissions	88	66	55
Card and digital banking fees	67	50	41
Trust services and investment management	51	39	30
Other service charges and fees	23	18	16
Securities gains (losses), net	0	0
Purchase accounting gain	0	0
Other income (loss)	52	40	37
Total noninterest income	438	345	293
Specialty Banking
Disaggregation of Revenue [Line Items]
Fixed income	406	422	278
Deposit transactions and cash management	12	11	11
Mortgage banking and title income	152	128	8
Brokerage, management fees and commissions	0	0	0
Card and digital banking fees	3	2	2
Trust services and investment management	0	0	0
Other service charges and fees	17	7	5
Securities gains (losses), net	0	0
Purchase accounting gain	0	0
Other income (loss)	7	6	11
Total noninterest income	597	576	315
Corporate
Disaggregation of Revenue [Line Items]
Fixed income	0	0	1
Deposit transactions and cash management	6	6	7
Mortgage banking and title income	2	1	2
Brokerage, management fees and commissions	0	0	0
Card and digital banking fees	8	8	6
Trust services and investment management	0	0	0
Other service charges and fees	4	1	0
Securities gains (losses), net	13	(6)
Purchase accounting gain	(1)	533
Other income (loss)	9	28	30
Total noninterest income	$ 41	$ 571	$ 46