Loans and Leases - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Loans And Leases Receivable [Line Items]
Commercial real estate loans held for sale	$ 39,000,000	$ 308,000,000
Residential mortgage loans securitized formerly held in Company's portfolio			$ 1,300,000,000
Automobile loans securitized and sold	0		1,400,000,000
Recognized gain			42,382,000
Recognized gain sale of securities			20,683,000
Charges incurred for reimbursement of loan	5,000,000	4,000,000	17,000,000
Contractual principal and interest payments	768,000,000	198,000,000
Interest income that would have been recognized on nonaccrual and renegotiated loans if those loans were accruing interest at their originally contracted terms	56,784,000	58,314,000	62,010,000
Interest on nonaccrual and renegotiated loans included in interest income	30,735,000	28,492,000	$ 31,987,000
Guaranteed amount included in the estimated residual value of leased assets associated with direct financing leases	50,000,000	48,000,000
Amount of foreclosed residential real estate property held	172,000,000	$ 44,000,000
Loans secured by residential real estate that were in the process of foreclosure	$ 315,000,000
Maximum [Member]
Loans And Leases Receivable [Line Items]
Purchased impaired loans as a percentage of total assets	1.00%	1.00%
Director and Certain Officers [Member]
Loans And Leases Receivable [Line Items]
Exclusion limit of loans from related party disclosure	Less than $120,000
Borrowing by directors and certain officers of M&T and its banking subsidiaries and their associates	$ 52,152,000	$ 49,799,000
New borrowings by directors, certain officers and their associates	4,425,000
Repayments and other reductions of borrowings by directors, certain officers and their associates	2,072,000
Commercial Real Estate [Member]
Loans And Leases Receivable [Line Items]
Loans serviced for others sold with credit recourse	2,500,000,000
Loans pledged to secure outstanding borrowings from the FHLB of New York	10,400,000,000
Residential Mortgage Loans [Member]
Loans And Leases Receivable [Line Items]
Mortgage loans held for sale	353,000,000	$ 435,000,000
Loans pledged to secure outstanding borrowings from the FHLB of New York	20,900,000,000
Commercial Loans and Leases [Member]
Loans And Leases Receivable [Line Items]
Loans pledged to secure outstanding borrowings from the FHLB of New York	11,100,000,000
Home Equity Loans and Lines of Credit [Member]
Loans And Leases Receivable [Line Items]
Loans pledged to secure outstanding borrowings from the FHLB of New York	3,900,000,000
Other Consumer Loans [Member]
Loans And Leases Receivable [Line Items]
Loans pledged to secure outstanding borrowings from the FHLB of New York	$ 3,600,000,000