Revenue from contracts with customers - Summary of Sources of Noninterest Income that are Subject to Revenue Recognition Accounting Guidance (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	$ 417	$ 388	$ 814	$ 755
Service charges on deposit accounts
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	137	127	270	251
Trust income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	182	170	359	330
Brokerage services income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	31	30	63	59
Merchant discount and credit card interchange fees
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	46	43	83	80
Other
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	21	18	39	35
Commercial Bank
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	76	68	148	136
Commercial Bank \| Service charges on deposit accounts
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	43	40	88	80
Commercial Bank \| Trust income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	1	1	2	2
Commercial Bank \| Brokerage services income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	2	1	3	3
Commercial Bank \| Merchant discount and credit card interchange fees
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	19	19	35	36
Commercial Bank \| Other
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	11	7	20	15
Retail Bank
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	129	119	245	230
Retail Bank \| Service charges on deposit accounts
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	94	87	182	171
Retail Bank \| Trust income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Retail Bank \| Brokerage services income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Retail Bank \| Merchant discount and credit card interchange fees
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	27	24	48	44
Retail Bank \| Other
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	8	8	15	15
Institutional Services and Wealth Management
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	212	201	421	389
Institutional Services and Wealth Management \| Service charges on deposit accounts
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Institutional Services and Wealth Management \| Trust income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	181	169	357	328
Institutional Services and Wealth Management \| Brokerage services income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	29	29	60	56
Institutional Services and Wealth Management \| Merchant discount and credit card interchange fees
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Institutional Services and Wealth Management \| Other
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	$ 2	$ 3	$ 4	$ 5