Business Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Noninterest income:
Deposit transactions and cash management	$ 44	$ 45	$ 88	$ 87
Fixed income	40	30	92	69
Brokerage, management fees and commissions	25	22	49	44
Card and digital banking fees	20	21	38	40
Other service charges and fees	14	14	27	27
Trust services and investment management	12	12	24	24
Mortgage banking income	10	6	19	11
Gain on merger termination	0	225	0	225
Securities gains (losses), net	1	0	1	1
Other income	20	25	43	43
Total noninterest income	186	400	381	571
Revenue from contract with customer	9	9
Underwriting, portfolio advisory, and other noninterest income
Noninterest income:
Revenue from contract with customer			20	19
Regional Banking
Noninterest income:
Deposit transactions and cash management	39	40	78	77
Fixed income	0	0	0	0
Brokerage, management fees and commissions	25	22	49	44
Card and digital banking fees	17	18	34	35
Other service charges and fees	6	6	12	13
Trust services and investment management	12	12	24	24
Mortgage banking income	0	0	0	0
Gain on merger termination		0		0
Securities gains (losses), net	0		0	0
Other income	10	8	17	17
Total noninterest income	109	106	214	210
Specialty Banking
Noninterest income:
Deposit transactions and cash management	3	3	6	6
Fixed income	40	31	92	70
Brokerage, management fees and commissions	0	0	0	0
Card and digital banking fees	1	1	1	1
Other service charges and fees	8	8	15	14
Trust services and investment management	0	0	0	0
Mortgage banking income	10	6	19	11
Gain on merger termination		0		0
Securities gains (losses), net	0		0	0
Other income	2	1	4	4
Total noninterest income	64	50	137	106
Corporate
Noninterest income:
Deposit transactions and cash management	2	2	4	4
Fixed income	0	(1)	0	(1)
Brokerage, management fees and commissions	0	0	0	0
Card and digital banking fees	2	2	3	4
Other service charges and fees	0	0	0	0
Trust services and investment management	0	0	0	0
Mortgage banking income	0	0	0	0
Gain on merger termination		225		225
Securities gains (losses), net	1		1	1
Other income	8	16	22	22
Total noninterest income	$ 13	$ 244	$ 30	$ 255