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, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	$ 442	$ 417	$ 860	$ 814
Service charges on deposit accounts
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	144	137	283	270
Trust income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	197	182	380	359
Brokerage services income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	35	31	70	63
Merchant discount and credit card interchange fees
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	45	46	82	83
Other
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	21	21	45	39
Commercial Bank
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	78	76	157	148
Commercial Bank \| Service charges on deposit accounts
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	46	43	93	88
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	2	3	3
Commercial Bank \| Merchant discount and credit card interchange fees
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	18	19	33	35
Commercial Bank \| Other
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	11	11	26	20
Retail Bank
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	133	129	254	245
Retail Bank \| Service charges on deposit accounts
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	98	94	190	182
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	27	49	48
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	231	212	449	421
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	196	181	378	357
Institutional Services and Wealth Management \| Brokerage services income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	33	29	67	60
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	$ 2	$ 4	$ 4