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Loans and allowance for loan losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Millions | Sep. 30, 2025 | Jun. 30, 2025 | Jan. 01, 2025 | Dec. 31, 2024 | Sep. 30, 2024 | Jun. 30, 2024 | Jan. 01, 2024
--- | --- | --- | --- | --- | --- | --- | ---
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Amortized Cost |  | $ 1,512 | $ 1,573 | $ 1,690 | $ 1,690 | $ 1,926 | $ 2,024 | $ 2,166
Total | [1] | 136,974 |  |  | 135,581 |  |  |
Unamortized loan cost (fee) and purchase premium (discount) |  | (279) |  |  | 277 |  |  |
Financing receivable, accrued interest, before allowance for credit loss |  | 619 |  |  | 628 |  |  |
Current |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 133,830 |  |  | 131,898 |  |  |
30-89 Days Past Due |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 1,200 |  |  | 1,655 |  |  |
Accruing Loans Past Due 90 Days or More |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 432 |  |  | 338 |  |  |
Commercial and industrial |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Amortized Cost |  | 760 | 787 | 696 | 696 | 810 | 805 | 670
Total |  | 61,887 |  |  | 61,481 |  |  |
Commercial and industrial | Current |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 60,952 |  |  | 60,374 |  |  |
Commercial and industrial | 30-89 Days Past Due |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 172 |  |  | 399 |  |  |
Commercial and industrial | Accruing Loans Past Due 90 Days or More |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 3 |  |  | 12 |  |  |
Commercial Real Estate | Commercial |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Amortized Cost |  | 361 | 376 | 468 | 468 | 578 | 707 | 869
Total |  | 20,062 |  |  | 20,780 |  |  |
Mortgage loans held for sale |  | 278 |  |  | 310 |  |  |
Commercial Real Estate | Commercial | Current |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 19,493 |  |  | 20,054 |  |  |
Commercial Real Estate | Commercial | 30-89 Days Past Due |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 189 |  |  | 255 |  |  |
Commercial Real Estate | Commercial | Accruing Loans Past Due 90 Days or More |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 19 |  |  | 3 |  |  |
Commercial Real Estate | Residential builder and developer |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Amortized Cost |  | 0 | 1 | 2 | 2 | 2 | 2 | 3
Total |  | 92 |  |  | 835 |  |  |
Mortgage loans held for sale |  | 661 |  |  |  |  |  |
Commercial Real Estate | Residential builder and developer | Current |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 80 |  |  | 830 |  |  |
Commercial Real Estate | Residential builder and developer | 30-89 Days Past Due |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 12 |  |  | 3 |  |  |
Commercial Real Estate | Residential builder and developer | Accruing Loans Past Due 90 Days or More |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 0 |  |  | 0 |  |  |
Commercial Real Estate | Other commercial construction |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Amortized Cost |  | 21 | 23 | 66 | 66 | 84 | 77 | 171
Total |  | 3,892 |  |  | 5,149 |  |  |
Commercial Real Estate | Other commercial construction | Current |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 3,859 |  |  | 5,018 |  |  |
Commercial Real Estate | Other commercial construction | 30-89 Days Past Due |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 12 |  |  | 65 |  |  |
Commercial Real Estate | Other commercial construction | Accruing Loans Past Due 90 Days or More |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 0 |  |  | 0 |  |  |
Commercial Real Estate | Other Revenue Portfolio Segment |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Mortgage loans held for sale |  | 15 |  |  |  |  |  |
Residential Real Estate | Residential |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Amortized Cost |  | 250 | 265 | 279 | 279 | 276 | 260 | 270
Total |  | 24,662 |  |  | 23,166 |  |  |
Mortgage loans held for sale |  | 327 |  |  | 211 |  |  |
Residential Real Estate | Residential | Current |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 23,395 |  |  | 21,853 |  |  |
Total |  | 23,395 |  |  | 21,853 |  |  |
Residential Real Estate | Residential | 30-89 Days Past Due |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 615 |  |  | 719 |  |  |
Residential Real Estate | Residential | Accruing Loans Past Due 90 Days or More |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 402 |  |  | 315 |  |  |
Total |  | 402 |  |  | 315 |  |  |
Consumer | Home equity lines and loans |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Amortized Cost |  | 77 | 75 | 81 | 81 | 82 | 79 | 81
Total |  | 4,730 |  |  | 4,592 |  |  |
Consumer | Home equity lines and loans | Current |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 4,622 |  |  | 4,482 |  |  |
Total |  | 4,622 |  |  | 4,482 |  |  |
Consumer | Home equity lines and loans | 30-89 Days Past Due |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 31 |  |  | 29 |  |  |
Consumer | Home equity lines and loans | Accruing Loans Past Due 90 Days or More |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 0 |  |  | 0 |  |  |
Total |  | 0 |  |  | 0 |  |  |
Consumer | Recreational finance |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Amortized Cost |  | 29 | 25 | 31 | 31 | 28 | 25 | 36
Total |  | 14,152 |  |  | 12,564 |  |  |
Consumer | Recreational finance | Current |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 14,032 |  |  | 12,429 |  |  |
Total |  | 14,032 |  |  | 12,429 |  |  |
Consumer | Recreational finance | 30-89 Days Past Due |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 91 |  |  | 104 |  |  |
Consumer | Recreational finance | Accruing Loans Past Due 90 Days or More |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 0 |  |  | 0 |  |  |
Total |  | 0 |  |  | 0 |  |  |
Consumer | Automobile |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Amortized Cost |  | 10 | 9 | 12 | 12 | 11 | 11 | 14
Total |  | 5,223 |  |  | 4,794 |  |  |
Consumer | Automobile | Current |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 5,157 |  |  | 4,724 |  |  |
Total |  | 5,157 |  |  | 4,724 |  |  |
Consumer | Automobile | 30-89 Days Past Due |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 56 |  |  | 58 |  |  |
Consumer | Automobile | Accruing Loans Past Due 90 Days or More |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 0 |  |  | 0 |  |  |
Total |  | 0 |  |  | 0 |  |  |
Consumer | Other |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Amortized Cost |  | 4 | $ 12 | $ 55 | 55 | $ 55 | $ 58 | $ 52
Total |  | 2,274 |  |  | 2,220 |  |  |
Consumer | Other | Current |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 2,240 |  |  | 2,134 |  |  |
Consumer | Other | 30-89 Days Past Due |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | 22 |  |  | 23 |  |  |
Consumer | Other | Accruing Loans Past Due 90 Days or More |  |  |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |  |  |
Loans |  | $ 8 |  |  | $ 8 |  |  |
[1] | Loans of $2.3 billion and $1.5 billion at September 30, 2025 and December 31, 2024, respectively, were held in special purpose trusts to settle the respective obligations of asset-backed notes issued by those trusts. The outstanding balances of those asset-backed notes issued to third party investors were included in Long-term borrowings and were $1.9 billion at September 30, 2025 and $1.2 billion at December 31, 2024.

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