Loans and leases and allowance for credit losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized Cost	$ 1,690	$ 2,166	$ 2,439	$ 2,060
Total	135,581	134,068
Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	131,898	129,839
30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,655	1,724
Accruing Loans Past Due 90 Days or More
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	338	339
Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized Cost	696	670	504	371
Total	61,481	57,010
Commercial Portfolio Segment | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	60,374	56,091
Commercial Portfolio Segment | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	399	238
Commercial Portfolio Segment | Accruing Loans Past Due 90 Days or More
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	12	11
Commercial Real Estate | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized Cost	468	869	1,240	919
Total	20,780	25,277
Commercial Real Estate | Residential builder and developer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized Cost	2	3	1	3
Total	835	1,073
Commercial Real Estate | Other commercial construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized Cost	66	171	125	111
Total	5,149	6,653
Commercial Real Estate | Current | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	20,054	24,072
Commercial Real Estate | Current | Residential builder and developer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	830	1,065
Commercial Real Estate | Current | Other commercial construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,018	6,322
Commercial Real Estate | 30-89 Days Past Due | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	255	311
Commercial Real Estate | 30-89 Days Past Due | Residential builder and developer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3	5
Commercial Real Estate | 30-89 Days Past Due | Other commercial construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	65	159
Commercial Real Estate | Accruing Loans Past Due 90 Days or More | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3	25
Commercial Real Estate | Accruing Loans Past Due 90 Days or More | Residential builder and developer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Commercial Real Estate | Accruing Loans Past Due 90 Days or More | Other commercial construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	1
Residential Real Estate | Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized Cost	279	270	350	479
Total	23,166	23,264
Residential Real Estate | Current | Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	21,853	21,905
Total	21,853	21,905
Residential Real Estate | 30-89 Days Past Due | Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	719	794
Residential Real Estate | Accruing Loans Past Due 90 Days or More | Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	315	295
Total	315	295
Consumer: | Home equity lines and loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized Cost	81	81	85	70
Total	4,592	4,649
Consumer: | Recreational finance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized Cost	31	36	45	28
Total	12,564	10,058
Consumer: | Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized Cost	12	14	40	34
Total	4,794	3,992
Consumer: | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized Cost	55	52	$ 49	$ 45
Total	2,220	2,092
Consumer: | Current | Home equity lines and loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,482	4,528
Total	4,482	4,528
Consumer: | Current | Recreational finance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	12,429	9,935
Total	12,429	9,935
Consumer: | Current | Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,724	3,918
Total	4,724	3,918
Consumer: | Current | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,134	2,003
Consumer: | 30-89 Days Past Due | Home equity lines and loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	29	40
Consumer: | 30-89 Days Past Due | Recreational finance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	104	87
Consumer: | 30-89 Days Past Due | Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	58	60
Consumer: | 30-89 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	23	30
Consumer: | Accruing Loans Past Due 90 Days or More | Home equity lines and loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Total	0	0
Consumer: | Accruing Loans Past Due 90 Days or More | Recreational finance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Total	0	0
Consumer: | Accruing Loans Past Due 90 Days or More | Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Total	0	0
Consumer: | Accruing Loans Past Due 90 Days or More | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 8	$ 7