Loans and Leases and the Allowance for Credit Losses - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Loans And Leases Receivable [Line Items]
Commercial real estate loans held for sale	$ 167	$ 22
Contractual principal and interest payments	$ 378	410
Minimum delinquency period for loan level collectability analysis consumer mortgage	150 days
Amount of foreclosed residential real estate property held	$ 100	108
Loans secured by residential real estate that were in the process of foreclosure	$ 458	497
Percentage loans in the process of foreclosure, serviced by other entities, classified as purchased impaired	41.00%
Percentage loans in the process of foreclosure, serviced by other entities, classified as government guaranteed	21.00%
Residential Mortgage Loans [Member]
Loans And Leases Receivable [Line Items]
Mortgage loans held for sale	$ 288	356
Carrying value of loans for which partial charge-off has been recognized	33	34
Mortgage loans on real real estate not requiring charge off due to collateral carrying amount	19	20
Home Equity Loans and Lines of Credit [Member]
Loans And Leases Receivable [Line Items]
Carrying value of loans for which partial charge-off has been recognized	25	25
Mortgage loans on real real estate not requiring charge off due to collateral carrying amount	$ 29	$ 32
Maximum [Member]
Loans And Leases Receivable [Line Items]
Purchased impaired loans as a percentage of total assets	1.00%	1.00%
Minimum [Member]
Loans And Leases Receivable [Line Items]
Loan delinquent period	90 days

The threshold number of days in delinquency at which criticized loans are generally classified as non-accrual.

No definition available.

Name:	mtb_LoanDelinquentPeriodForNonAccrualStatusClassification
Namespace Prefix:	mtb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of purchased impaired loans as a percentage of total assets.

+ References

No definition available.

+ Details

Name:	mtb_LoansAcquiredInTransferImpairedAsPercentageOfAssets
Namespace Prefix:	mtb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Loans and leases receivable.

+ References

No definition available.

+ Details

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

- Definition

Loans and leases receivable net of partial charge off.

+ References

No definition available.

+ Details

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

- Definition

Minimum delinquency period threshold at which residential real estate loans and outstanding balances of home equity lines of credit are generally evaluated for collectability on a loan-by-loan basis giving consideration to estimated collateral values.

+ References

No definition available.

+ Details

Name:	mtb_MinimumDelinquencyPeriodForLoanLevelCollectabilityAnalysisConsumerMortgage
Namespace Prefix:	mtb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The carrying amount of the outstanding balance due under mortgage loans that were more than 150 days past due but did not require a partial charge off because the net realizable value of the collateral exceeded the outstanding customer balance.

+ References

No definition available.

+ Details

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

- Definition

Percentage of loans in the process of foreclosure, serviced by other entities, classified as government guaranteed.

+ References

No definition available.

+ Details

Name:	mtb_PercentageOfLoansInTheProcessOfForeclosureServicedByOtherEntitiesClassifiedAsGovernmentGuaranteed
Namespace Prefix:	mtb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of loans in the process of foreclosure, serviced by other entities, classified as purchased impaired.

+ References

No definition available.

+ Details

Name:	mtb_PercentageOfLoansInTheProcessOfForeclosureServicedByOtherEntitiesClassifiedAsPurchasedImpaired
Namespace Prefix:	mtb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Residential mortgage loans secured by residential real estate in process of foreclosure.

+ References

No definition available.

+ Details

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

- Definition

Fair value at acquisition of 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=82894507&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)(3)
-URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544

+ Details

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

- Definition

Amount, after allowance for bad debt, of commercial mortgage loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

+ Details

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

- Definition

Amount, after allowance for bad debt, of mortgage loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.

+ References

+ Details

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

- Definition

Carrying amount as of the balance sheet date of other real estate and foreclosed assets. Other real estate may include real estate investments, real estate loans that qualify as investments in real estate, and premises that are no longer used in operations may also be included in real estate owned. Foreclosed assets include all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10(4))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_HomeEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: