Business Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Noninterest income:
Fixed income	$ 52	$ 39
Deposit transactions and cash management	44	42
Brokerage, management fees and commissions	24	22
Card and digital banking fees	19	20
Other service charges and fees	13	13
Trust services and investment management	11	11
Mortgage banking income	9	5
Other income	22	19
Total noninterest income	194	171
Underwriting, portfolio advisory, and other noninterest income
Noninterest income:
Revenue from contract with customer	10	10
Regional Banking
Noninterest income:
Fixed income	0	0
Deposit transactions and cash management	39	37
Brokerage, management fees and commissions	24	22
Card and digital banking fees	16	17
Other service charges and fees	6	6
Trust services and investment management	11	11
Mortgage banking income	0	0
Other income	9	11
Total noninterest income	105	104
Specialty Banking
Noninterest income:
Fixed income	52	39
Deposit transactions and cash management	3	3
Brokerage, management fees and commissions	0	0
Card and digital banking fees	1	1
Other service charges and fees	7	7
Trust services and investment management	0	0
Mortgage banking income	9	5
Other income	0	1
Total noninterest income	72	56
Corporate
Noninterest income:
Fixed income	0	0
Deposit transactions and cash management	2	2
Brokerage, management fees and commissions	0	0
Card and digital banking fees	2	2
Other service charges and fees	0	0
Trust services and investment management	0	0
Mortgage banking income	0	0
Other income	13	7
Total noninterest income	$ 17	$ 11