Loans and Leases - Summary of Changes in Accretable Yield for Acquired Loans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Purchased Impaired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	$ 37,230	$ 42,252	$ 30,805
Interest income	(21,263)	(36,727)	(40,551)
Reclassifications from nonaccretable balance, net	60,551	31,705	51,998
Balance at end of period	76,518	37,230	42,252
Other [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	538,633	638,272	807,960
Interest income	(178,670)	(247,295)	(295,654)
Reclassifications from nonaccretable balance, net	24,907	149,595	148,490
Other	12,509	(1,939)	(22,524)
Balance at end of period	$ 397,379	$ 538,633	$ 638,272

The amount of interest from acquired loans included in earnings.

No definition available.

Name:	mtb_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldInterestIncome
Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This item represents other changes in the accretable yield due to changes in expected cash flows including changes in interest rates and prepayment assumptions.

+ References

No definition available.

+ Details

Name:	mtb_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldInterestOtherIncreaseDecrease
Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of the excess of a loan's cash flows expected to be collected over the investor's initial investment in acquired loans not accounted for as debt securities with evidence of deterioration of credit quality.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 15

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=27045933&loc=d3e13503-111538

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(2)

-URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544

+ Details

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

- Details

Name:	us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldMovementScheduleRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of reclassification (to) from nonaccretable difference (from) to the excess of a loan's cash flows expected to be collected over the investor's initial investment in acquired loans not accounted for as debt securities with evidence of deterioration of credit quality.

+ References

+ Details

Name:	us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldReclassificationsToFromNonaccretableDifference
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=mtb_PurchasedImpairedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_OtherCreditDerivativesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: