Fair value measurements - Quantitative Information Related to Significant Unobservable Inputs (Detail) (USD $)	12 Months Ended
Dec. 31, 2012
Privately issued residential [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Investments	$ 1,023,886
Valuation technique	Discounted cash flow
Unobservable inputs/ assumptions	Probability of default Loss severity
Probability of default weighted-average	19.00%
Loss severity weighted-average	51.00%
Privately issued residential [Member] \| Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Probability of default	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	40.00%
Loss severity	82.00%
Collateralized debt obligations [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Investments	61,869
Valuation technique	Discounted cash flow
Unobservable inputs/ assumptions	Probability of default Loss severity
Probability of default weighted-average	12.00%
Collateralized debt obligations [Member] \| Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Probability of default	0.00%
Loss severity	100.00%
Collateralized debt obligations [Member] \| Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Probability of default	65.00%
Net other assets (liabilities) [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Investments	$ 47,859
Valuation technique	Discounted cash flow
Unobservable inputs/ assumptions	Commitment expirations
Commitment expirations weighted-average	20.00%
Net other assets (liabilities) [Member] \| Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Commitment expirations	0.00%
Net other assets (liabilities) [Member] \| Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Commitment expirations	69.00%

Percentage of fair value inputs commitment expirations.

No definition available.

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- Definition

Percentage of fair value inputs loss severity.

+ References

No definition available.

+ Details

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- Definition

Percentage of fair value inputs probability of default.

+ References

No definition available.

+ Details

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- Definition

Weighted average percentage of fair value inputs commitment expirations.

+ References

No definition available.

+ Details

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Namespace Prefix:	mtb_
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- Definition

Weighted average percentage of fair value inputs loss severity.

+ References

No definition available.

+ Details

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- Definition

Weighted average percentage of fair value inputs probability of default

+ References

No definition available.

+ Details

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- Details

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- 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

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- Definition

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

+ References

+ Details

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- 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.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant