Fair value measurements (Details 2) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	6 Months Ended
Jun. 30, 2012
Quantitative information related to significant unobservable inputs
Investments	$ 1,169,668
Privately issued residential [Member]
Quantitative information related to significant unobservable inputs
Investments	1,080,519
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] \| Maximum [Member]
Quantitative information related to significant unobservable inputs
Probability of default Loss	49.00%
Loss severity	75.00%
Privately issued residential [Member] \| Minimum [Member]
Quantitative information related to significant unobservable inputs
Probability of default Loss	1.00%
Loss severity	32.00%
Collateralized Debt Obligations [Member]
Quantitative information related to significant unobservable inputs
Investments	55,098
Valuation technique	Discounted cash flow
Unobservable inputs/ assumptions	Probability of default
Probability of default weighted average	14.00%
Collateralized Debt Obligations [Member] \| Maximum [Member]
Quantitative information related to significant unobservable inputs
Probability of default Loss	65.00%
Collateralized Debt Obligations [Member] \| Minimum [Member]
Quantitative information related to significant unobservable inputs
Probability of default Loss	3.00%
Loss severity	100.00%
Commitments to originate real estate loans [Member]
Quantitative information related to significant unobservable inputs
Investments	34,051
Valuation technique	Discounted cash flow
Unobservable inputs/ assumptions	Commitment expirations
Commitment expirations weighted average	18.00%
Commitments to originate real estate loans [Member] \| Maximum [Member]
Quantitative information related to significant unobservable inputs
Commitment expirations	69.00%
Commitments to originate real estate loans [Member] \| Minimum [Member]
Quantitative information related to significant unobservable inputs
Commitment expirations	0.00%
Privately issued commercial [Member]
Quantitative information related to significant unobservable inputs
Investments	$ 12,127

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

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- Definition

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

+ References

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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