Significant accounting policies (Policies)	3 Months Ended
Significant accounting policies (Policies)	Mar. 31, 2015
Accounting Policies [Abstract]
Consolidation	The consolidated financial statements of M&T Bank Corporation (“M&T”) and subsidiaries (“the Company”) were compiled in accordance with generally accepted accounting principles (“GAAP”) using the accounting policies set forth in note 1 of Notes to Financial Statements included in the 2014 Annual Report. Additionally, effective January 1, 2015 the Company made an accounting policy election in accordance with amended accounting guidance issued by the Financial Accounting Standards Board in January 2014 to account for investments in qualified affordable housing projects using the proportional amortization method. Under the proportional amortization method, the Company amortizes the initial cost of the investment in proportion to the tax credits and other tax benefits received and recognizes the net investment performance in the income statement as a component of income tax expense. The adoption of the amended guidance did not have a significant effect on the Company’s financial position or results of operation, but did result in the restatement of the consolidated statement of income for the three-month period ended March 31, 2014 to remove $12 million of losses associated with qualified affordable housing projects from “other costs of operations” and include the amortization of the initial cost of the investment in income tax expense. The cumulative effect adjustment associated with adopting the amended guidance was not material as of the beginning of any period presented in these consolidated financial statements. See note 11 for information regarding the Company’s investments in qualified affordable housing projects. In the opinion of management, all adjustments necessary for a fair presentation have been made and, except as described above, were all of a normal recurring nature.

Disclosure of accounting policy regarding (1) the principles it follows in consolidating or combining the separate financial statements, including the principles followed in determining the inclusion or exclusion of subsidiaries or other entities in the consolidated or combined financial statements and (2) its treatment of interests (for example, common stock, a partnership interest or other means of exerting influence) in other entities, for example consolidation or use of the equity or cost methods of accounting. The accounting policy may also address the accounting treatment for intercompany accounts and transactions, noncontrolling interest, and the income statement treatment in consolidation for issuances of stock by a subsidiary.

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