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Significant accounting policies | 9 Months Ended
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Sep. 30, 2025
Accounting Policies [Abstract] |
Significant accounting policies | 1. Significant accounting policies The consolidated interim financial statements of the Company were compiled in accordance with GAAP using the accounting policies set forth in note 1 of Notes to Financial Statements included in M&T's 2024 Annual Report. The financial statements contain all adjustments which are, in the opinion of management, necessary for a fair statement of the Company's financial position, results of operations and cash flows for the interim periods presented. The following table provides a description of accounting standards applicable to M&T but not yet adopted at September 30, 2025. Recent accounting developments
| Standard |  |  | Description |  |  | Required date of adoption |  |  | Effect on consolidated financial statements |
| Standards not yet adopted as of September 30, 2025 |
| Income Taxes - Improvements to income tax disclosures |  |  | The standard requires enhanced disclosures in the notes to financial statements including income taxes paid by jurisdiction (federal, state, foreign) and a tabular rate reconciliation between the reported amount of income tax expense (or benefit) and the amount of statutory federal income tax at current rates. |  |  | December 31, 2025 |  |  | The Company intends to make the required disclosures of the amended guidance in its consolidated financial statements for the year ended December 31, 2025. |
| Income Statement - Expense disaggregation disclosures |  |  | The standard requires disclosure in the notes to financial statements of specified information about certain cost and expense captions on the income statement. |  |  | January 1, 2027 |  |  | The Company does not expect the guidance will have a material impact on its consolidated financial statements. |
| Targeted improvements to the accounting for internal-use software |  |  | The standard eliminates the concept of a software development project stage such that the guidance is agnostic to different software development methods and introduces a new threshold for cost capitalization. The standard also provides factors to consider when determining whether significant development uncertainty exists. |  |  | January 1, 2028 |  |  | The Company is evaluating the impact of the standard but does not expect the guidance will have a material impact on its consolidated financial statements. |

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- Definition The entire disclosure for all significant accounting policies of the reporting entity. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 235 -Name Accounting Standards Codification -Publisher FASB -URI https://asc.fasb.org/235/tableOfContent Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483426/235-10-50-1 + Details
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