Name:	mtb_GrossRealizedGainLossOnSaleOfInvestmentSecurities
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Gross realized gain loss on securities.

No definition available.

Name:	mtb_GrossRealizedGainLossOnSecurities
Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
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Total amount of accumulated unrealized gain on investments in debt and equity securities before taxes.

No definition available.

Name:	mtb_InvestmentSecuritiesGrossUnrealizedLosses
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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Carrying value of investment securities pledged to secure borrowings from certain various FHLBs, repurchase agreements, governmental deposits, interest rate swap agreements and available lines of credit.

No definition available.

Name:	mtb_InvestmentSecuritiesPledgedToSecureDebtCarryingValue
Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The number of individual investment securities in gross unrealized loss positions. Unrealized losses occur when the amortized cost of an investment security is greater than its estimated fair value.

No definition available.

Name:	mtb_NumberOfInvestmentSecuritiesWithGrossLosses
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Number of single investment securities that exceeded ten percent of shareholders' equity.

No definition available.

Name:	mtb_NumberOfSingleInvestmentSecuritiesThatExceededTenPercentOfShareholdersEquity
Namespace Prefix:	mtb_
Data Type:	xbrli:integerItemType
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Amount, after adjustment, of cost-method investment. Adjustments include, but are not limited to, dividends received in excess of earnings after date of investment that are considered a return of investment and other than temporary impairments.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 325
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=75025870&loc=d3e40691-111596

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 325
-SubTopic 20
-Section 35
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=75027002&loc=d3e40346-111594

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The difference between the carrying value and the sale price of an investment. A gain would be recognized when the sale price of the investment is greater than the carrying value of the investment. This element refers to the Gain included in earnings and not to the cash proceeds of the sale.

No definition available.

Name:	us-gaap_GainOnSaleOfInvestments
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Data Type:	xbrli:monetaryItemType
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_InvestmentHoldingsLineItems
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Data Type:	xbrli:stringItemType
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Period Type:	duration

The carrying amount (fair value) as of the balance sheet date of securities held that had been pledged by counterparties under financing and lending arrangements, pursuant to which the entity has the right by agreement or custom to sell or re-pledge such securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5086-111524

Name:	us-gaap_SecuritiesHeldAsCollateralAtFairValue
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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Name:	us-gaap_DebtSecurityAxis=us-gaap_CollateralizedDebtObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_InvestmentTypeAxis=mtb_FannieMaeAndFreddieMacPreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_ForeignGovernmentDebtSecuritiesMember
Namespace Prefix:
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