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
Mar. 31, 2026	Mar. 31, 2025
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	$ 418	$ 397
Service charges on deposit accounts
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	139	133
Trust income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	183	177
Brokerage services income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	35	32
Merchant discount and credit card interchange fees
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	37	37
Other
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	24	18
Commercial Bank
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	79	72
Commercial Bank \| Service charges on deposit accounts
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	47	45
Commercial Bank \| Trust income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	1	1
Commercial Bank \| Brokerage services income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	1	1
Commercial Bank \| Merchant discount and credit card interchange fees
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	15	16
Commercial Bank \| Other
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	15	9
Retail Bank
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	121	116
Retail Bank \| Service charges on deposit accounts
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	92	88
Retail Bank \| Trust income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	0	0
Retail Bank \| Brokerage services income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	0	0
Retail Bank \| Merchant discount and credit card interchange fees
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	22	21
Retail Bank \| Other
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	7	7
Institutional Services and Wealth Management
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	218	209
Institutional Services and Wealth Management \| Service charges on deposit accounts
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	0	0
Institutional Services and Wealth Management \| Trust income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	182	176
Institutional Services and Wealth Management \| Brokerage services income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	34	31
Institutional Services and Wealth Management \| Merchant discount and credit card interchange fees
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	0	0
Institutional Services and Wealth Management \| Other
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	$ 2	$ 2