Loans and leases - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Loans And Leases Receivable [Line Items]
Charges incurred for reimbursement of loan	$ 28,000,000	$ 23,000,000	$ 30,000,000
Contractual principal and interest payments	447,000,000	653,000,000
Purchased impaired loans as a percentage of total assets	Less than 1% of the Company's assets	Less than 1% of the Company's assets
Interest income that would have been recognized on nonaccrual and renegotiated loans if those loans were accruing interest at their originally contracted terms	69,054,000	80,278,000	90,351,000
Interest on nonaccrual and renegotiated loans included in interest income	30,484,000	31,301,000	40,139,000
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	99,532,000	96,523,000
New borrowings by directors, certain officers and their associates	16,026,000
Repayments and other reductions of borrowings by directors, certain officers and their associates	13,017,000
Guaranteed amount included in the estimated residual value of leased assets associated with direct financing leases	54,000,000	52,000,000
Estimated residual value	137,570,000	144,275,000
Leveraged leases for which the company is indemnified from loss by AIB [Member]
Loans And Leases Receivable [Line Items]
Estimated residual value	7,000,000	13,000,000
Residential mortgage loans [Member]
Loans And Leases Receivable [Line Items]
Mortgage loans held for sale	1,200,000,000	210,000,000
Loans pledged to secure outstanding borrowings from the FHLB of New York	5,900,000,000
Commercial Real Estate [Member]
Loans And Leases Receivable [Line Items]
Commercial mortgage loans held for sale	200,000,000	161,000,000
Mortgage loans serviced for others sold with credit recourse	2,000,000,000
Loans pledged to secure outstanding borrowings from the FHLB of New York	9,600,000,000
Commercial loans and leases [Member]
Loans And Leases Receivable [Line Items]
Loans pledged to secure outstanding borrowings from the FHLB of New York	8,000,000,000
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	4,200,000,000
Other consumer loans [Member]
Loans And Leases Receivable [Line Items]
Loans pledged to secure outstanding borrowings from the FHLB of New York	$ 3,100,000,000