Derivative financial instruments (Details) (Fixed rate long-term borrowings [Member], USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
Jun. 30, 2012	Dec. 31, 2011
Fixed rate long-term borrowings [Member]
Information about interest rate swap agreements
Notional amount	$ 900,000	$ 900,000
Average maturity (in years)	4 years 10 months 24 days	5 years 4 months 24 days
Weighted-average rate, fixed	6.07%	6.07%
Weighted-average rate, variable	2.01%	2.07%

Name:	mtb_InformationAboutInterestRateSwapAgreementsAbstract
Namespace Prefix:	mtb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Average fixed interest rate related to the group of interest rate derivatives.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeAverageFixedInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeAverageRemainingMaturity1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Average variable interest rate related to the group of interest rate derivatives.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeAverageVariableInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Aggregate notional amount of all derivatives designated as a fair value hedging instrument. The notional amount relates to a number of currency units, shares, bushels, pounds, or other units specified in a derivative instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Notional Amount

-URI http://asc.fasb.org/extlink&oid=6519104

+ Details

Name:	us-gaap_NotionalAmountOfFairValueHedgeInstruments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant