Regulatory Matters - Additional Information (Detail) - USD ($)	Jan. 01, 2019	Dec. 31, 2017	Dec. 31, 2016
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Funds available for payment of dividends to M&T from banking subsidiaries		$ 397,000,000
Required subsidiary noninterest-earning reserves against certain deposit liabilities		$ 679,401,000	$ 594,831,000
Capital conservation buffer		1.25%	0.625%
Scenario Forecast [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital conservation buffer	2.50%
Maximum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Consolidated assets required per Federal Reserve Board to submit annual capital plans		$ 50,000,000,000