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		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	$ 423	$ 394	$ 1,237	$ 1,149
Service charges on deposit accounts
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	141	132	411	383
Trust income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	181	170	540	500
Brokerage services income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	34	32	97	91
Merchant discount and credit card interchange fees
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	47	41	130	121
Other
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	20	19	59	54
Commercial Bank
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	78	69	226	205
Commercial Bank \| Service charges on deposit accounts
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	45	40	133	120
Commercial Bank \| Trust income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	1	1	3	3
Commercial Bank \| Brokerage services income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	1	2	4	5
Commercial Bank \| Merchant discount and credit card interchange fees
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	20	18	55	54
Commercial Bank \| Other
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	11	8	31	23
Retail Bank
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	130	123	375	353
Retail Bank \| Service charges on deposit accounts
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	96	92	278	263
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	23	75	67
Retail Bank \| Other
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	7	8	22	23
Institutional Services and Wealth Management
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	215	202	636	591
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	180	169	537	497
Institutional Services and Wealth Management \| Brokerage services income
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	33	30	93	86
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	$ 6	$ 8