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Variable interest entities and asset securitizations - Additional Information (Detail) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Variable Interest Entity [Line Items] |  |  |
Loss on securitization of assets | $ 0 |  |
Loans and leases | 135,581,000,000 | $ 134,068,000,000 |
Long-term borrowings | 12,605,000,000 | 8,201,000,000 |
Other assets for its "investment" in the common securities recognized by the company of various trusts | 17,000,000 | 22,000,000 |
Total assets of partnerships in which the company invested | $ 208,105,000,000 | 208,264,000,000 |
Investment Program, Proportional Amortization Method, Elected, Income Tax Credit and Other Income Tax Benefit, before Amortization, Statement of Income or Comprehensive Income [Extensible Enumeration] | Interest Expense, Operating |  |
Investment Program, Proportional Amortization Method, Elected, Income Tax Credit and Other Income Tax Benefit, before Amortization, Statement of Cash Flows [Extensible Enumeration] | Interest Expense, Operating |  |
Investments amortized to income tax expense | $ 181,000,000 | 167,000,000 | $ 140,000,000
Variable Interest Entity Primary Beneficiary |  |  |
Variable Interest Entity [Line Items] |  |  |
Total assets of partnerships in which the company invested | 10,500,000,000 | 9,800,000,000 |
Federal tax credits and other federal tax benefits recognized | 38,000,000 | 26,000,000 | 22,000,000
Investments amortized to income tax expense | 181,000,000 | 167,000,000 | 140,000,000
Maximum exposure to loss of investments in real estate partnerships | 2,000,000,000.0 |  |
Variable Interest Entity Primary Beneficiary | Third Party Investors |  |  |
Variable Interest Entity [Line Items] |  |  |
Long-term borrowings |  | 1,200,000,000 |
Variable Interest Entity Primary Beneficiary | M&T Bank |  |  |
Variable Interest Entity [Line Items] |  |  |
Loans and leases | 1,500,000,000 |  |
Variable Interest Entity Primary Beneficiary | Renewable Energy |  |  |
Variable Interest Entity [Line Items] |  |  |
Federal tax credits and other federal tax benefits recognized | $ 34,000,000 | $ 33,000,000 | $ 17,000,000

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