| Document and Entity Information | Feb. 21, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | M&T BANK CORP |
| Amendment Flag | false |
| Entity Central Index Key | 0000036270 |
| Document Type | 8-K |
| Document Period End Date | Feb. 21, 2021 |
| Entity Incorporation State Country Code | NY |
| Entity File Number | 1-9861 |
| Entity Tax Identification Number | 16-0968385 |
| Entity Address, Address Line One | One M&T Plaza |
| Entity Address, City or Town | Buffalo |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 14203 |
| City Area Code | (716) |
| Local Phone Number | 635-4000 |
| Written Communications | true |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, $.50 par value |
| Trading Symbol | MTB |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
