Loans and leases (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Loans And Leases Receivable Leases [Line Items]
Lease payments receivable	$ 154,551,000	$ 164,818,000
Estimated residual value	144,275,000	179,777,000
Unearned income	53,847,000	63,154,000
Loans and leases and allowance for credit losses (Details) (Textual) [Abstract]
Charges incurred for reimbursement of loan	23,000,000	30,000,000	10,000,000
Contractual principal and interest payments	653,000,000	97,000,000
Purchased impaired loans as a percentage of total assets	Less than 1% of companys assets	Less than .2% of companys assets
Interest income that would have been recognized on nonaccrual and renegotiated loans if those loans were accruing interest at their originally contracted terms	80,278,000	90,351,000	99,618,000
Interest on nonaccrual and renegotiated loans included in interest income	31,301,000	40,139,000	43,920,000
Exclusion limit of loans from related party disclosure	Less than 120000
Borrowing by directors and certain officers of M&T and its banking subsidiaries and their associates	96,523,000	105,540,000
New borrowings by directors, certain officers and their associates	12,320,000
Repayments and other reductions of borrowings by directors, certain officers and their associates	21,337,000
Guaranteed amount included in the estimated residual value of leased assets associated with direct financing leases	52,000,000	53,000,000
Residential Mortgage Loans [Member]
Loans And Leases Receivable Leases [Line Items]
Mortgage loans held for sale	210,000,000	341,000,000
Mortgage loans serviced for others sold with credit recourse	13,000,000
Loans pledged to secure outstanding borrowings from the FHLB of New York	4,200,000,000
Leveraged leases for which the company is indemnified from loss by AIB [Member]
Loans And Leases Receivable Leases [Line Items]
Estimated residual value	13,000,000	26,000,000
Commercial, financial, leasing [Member]
Loans And Leases Receivable Leases [Line Items]
Commercial mortgage loans held for sale	161,000,000	204,000,000
Mortgage loans serviced for others sold with credit recourse	1,800,000,000
Loans pledged to secure outstanding borrowings from the FHLB of New York	8,500,000,000
Commercial Loans and Leases [Member]
Loans And Leases Receivable Leases [Line Items]
Loans pledged to secure outstanding borrowings from the FHLB of New York	6,100,000,000
Home Equity Loans and Lines of Credit [Member]
Loans And Leases Receivable Leases [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 Leases [Line Items]
Loans pledged to secure outstanding borrowings from the FHLB of New York	$ 3,200,000,000