Loans and leases and allowance for credit losses - Loan Modifications (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Financing Receivable, Modifications [Line Items]
Modified in period	$ 1,130	$ 1,586
Percent of Total Loan Class	0.83%	1.18%
Term Extension
Financing Receivable, Modifications [Line Items]
Modified in period	$ 1,001	$ 1,476
Other
Financing Receivable, Modifications [Line Items]
Modified in period	100	52
Combination of Modification Types
Financing Receivable, Modifications [Line Items]
Modified in period	29	58
Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Modified in period	$ 303	$ 198
Percent of Total Loan Class	0.49%	0.35%
Commercial Portfolio Segment | Term Extension
Financing Receivable, Modifications [Line Items]
Modified in period	$ 212	$ 169
Commercial Portfolio Segment | Other
Financing Receivable, Modifications [Line Items]
Modified in period	84	27
Commercial Portfolio Segment | Combination of Modification Types
Financing Receivable, Modifications [Line Items]
Modified in period	7	2
Commercial Real Estate | Commercial
Financing Receivable, Modifications [Line Items]
Modified in period	$ 515	$ 651
Percent of Total Loan Class	2.48%	2.57%
Commercial Real Estate | Residential builder and developer
Financing Receivable, Modifications [Line Items]
Modified in period	$ 2	$ 71
Percent of Total Loan Class	0.29%	6.63%
Commercial Real Estate | Other commercial construction
Financing Receivable, Modifications [Line Items]
Modified in period	$ 130	$ 488
Percent of Total Loan Class	2.53%	7.34%
Commercial Real Estate | Term Extension | Commercial
Financing Receivable, Modifications [Line Items]
Modified in period	$ 509	$ 610
Commercial Real Estate | Term Extension | Residential builder and developer
Financing Receivable, Modifications [Line Items]
Modified in period	2	69
Commercial Real Estate | Term Extension | Other commercial construction
Financing Receivable, Modifications [Line Items]
Modified in period	130	480
Commercial Real Estate | Other | Commercial
Financing Receivable, Modifications [Line Items]
Modified in period	2	0
Commercial Real Estate | Other | Residential builder and developer
Financing Receivable, Modifications [Line Items]
Modified in period	0	2
Commercial Real Estate | Other | Other commercial construction
Financing Receivable, Modifications [Line Items]
Modified in period	0	0
Commercial Real Estate | Combination of Modification Types | Commercial
Financing Receivable, Modifications [Line Items]
Modified in period	4	41
Commercial Real Estate | Combination of Modification Types | Residential builder and developer
Financing Receivable, Modifications [Line Items]
Modified in period	0	0
Commercial Real Estate | Combination of Modification Types | Other commercial construction
Financing Receivable, Modifications [Line Items]
Modified in period	0	8
Residential Real Estate | Residential
Financing Receivable, Modifications [Line Items]
Modified in period	$ 177	$ 177
Percent of Total Loan Class	0.76%	0.76%
Residential Real Estate | Term Extension | Residential
Financing Receivable, Modifications [Line Items]
Modified in period	$ 146	$ 148
Residential Real Estate | Other | Residential
Financing Receivable, Modifications [Line Items]
Modified in period	14	23
Residential Real Estate | Combination of Modification Types | Residential
Financing Receivable, Modifications [Line Items]
Modified in period	17	6
Consumer: | Home equity lines and loans
Financing Receivable, Modifications [Line Items]
Modified in period	$ 2	$ 1
Percent of Total Loan Class	0.04%	0.03%
Consumer: | Recreational finance
Financing Receivable, Modifications [Line Items]
Modified in period	$ 1	$ 0
Percent of Total Loan Class	0.01%	0.00%
Consumer: | Automobile
Financing Receivable, Modifications [Line Items]
Modified in period	$ 0	$ 0
Percent of Total Loan Class	0.00%	0.00%
Consumer: | Other
Financing Receivable, Modifications [Line Items]
Modified in period	$ 0	$ 0
Percent of Total Loan Class	0.00%	0.00%
Consumer: | Term Extension | Home equity lines and loans
Financing Receivable, Modifications [Line Items]
Modified in period	$ 1	$ 0
Consumer: | Term Extension | Recreational finance
Financing Receivable, Modifications [Line Items]
Modified in period	1	0
Consumer: | Term Extension | Automobile
Financing Receivable, Modifications [Line Items]
Modified in period	0	0
Consumer: | Term Extension | Other
Financing Receivable, Modifications [Line Items]
Modified in period	0	0
Consumer: | Other | Home equity lines and loans
Financing Receivable, Modifications [Line Items]
Modified in period	0	0
Consumer: | Other | Recreational finance
Financing Receivable, Modifications [Line Items]
Modified in period	0	0
Consumer: | Other | Automobile
Financing Receivable, Modifications [Line Items]
Modified in period	0	0
Consumer: | Other | Other
Financing Receivable, Modifications [Line Items]
Modified in period	0	0
Consumer: | Combination of Modification Types | Home equity lines and loans
Financing Receivable, Modifications [Line Items]
Modified in period	1	1
Consumer: | Combination of Modification Types | Recreational finance
Financing Receivable, Modifications [Line Items]
Modified in period	0	0
Consumer: | Combination of Modification Types | Automobile
Financing Receivable, Modifications [Line Items]
Modified in period	0	0
Consumer: | Combination of Modification Types | Other
Financing Receivable, Modifications [Line Items]
Modified in period	$ 0	$ 0