Fair value measurements - Quantitative Information Related to Significant Unobservable Inputs (Detail) (USD $)	9 Months Ended
Sep. 30, 2012
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Investments	$ 1,193,182
Privately issued residential [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Investments	1,065,636
Valuation technique	Discounted cash flow
Unobservable inputs/ assumptions	Probability of default Loss severity
Probability of default weighted average	18.00%
Loss severity weighted average	49.00%
Privately issued residential [Member] \| Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Probability of default Loss	1.00%
Loss severity	32.00%
Privately issued residential [Member] \| Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Probability of default Loss	40.00%
Loss severity	79.00%
Collateralized debt obligations [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Investments	57,201
Valuation technique	Discounted cash flow
Unobservable inputs/ assumptions	Probability of default Loss severity
Probability of default weighted average	15.00%
Collateralized debt obligations [Member] \| Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Probability of default Loss	3.00%
Loss severity	100.00%
Collateralized debt obligations [Member] \| Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Probability of default Loss	65.00%
Commitments to originate real estate loans [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Investments	$ 70,345
Valuation technique	Discounted cash flow
Unobservable inputs/ assumptions	Commitment expirations
Commitment expirations weighted average	22.00%
Commitments to originate real estate loans [Member] \| Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Commitment expirations	0.00%
Commitments to originate real estate loans [Member] \| Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Commitment expirations	73.00%

Percentage of fair value inputs commitment expirations.

No definition available.

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

- Definition

Percentage of fair value inputs loss severity.

+ References

No definition available.

+ Details

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

- Definition

Percentage of fair value inputs probability of default.

+ References

No definition available.

+ Details

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

- Definition

Weighted average percentage of fair value inputs commitment expirations.

+ References

No definition available.

+ Details

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

- Definition

Weighted average percentage of fair value inputs loss severity.

+ References

No definition available.

+ Details

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

- Definition

Weighted average percentage of fair value inputs probability of default

+ References

No definition available.

+ Details

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

- Details

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

- Definition

Description of significant assumptions used by management to measure fair value.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13433-108611

+ Details

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

- Definition

Description of the inputs and valuation technique(s) used to measure fair value.

+ References

+ Details

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

- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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