Fair value measurements (Details 1) (USD $) In Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance of other assets and other liabilities	$ 13,171	$ 20,843	$ 2,244	$ (80)
Total gains (losses) realized/ unrealized;
Included In Earnings of other assets and other liabilities	13,565	38,399	56,809	86,249
Transfer in and/or out of Level 3 of other assets and other liabilities	(18,799)	(32,825)	(51,116)	(59,752)
Ending Balance of other assets and other liabilities	7,937	26,417	7,937	26,417
Changes in unrealized gains (losses) included in earnings related to other assets and other liabilities still held at end of period	5,926	23,910	7,932	26,326
Privately issued residential [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	1,306,202	1,598,033	1,435,561	2,064,904
Total gains (losses) realized/ unrealized;
Included in earnings	(9,642)	(6,675)	(41,713)	(41,018)
Included in other comprehensive income	(4,030)	37,634	95,526	152,882
Settlements	(77,452)	(105,624)	(274,296)	(298,152)
Transfer in and/or out of Level 3				(355,248)
Ending Balance	1,215,078	1,523,368	1,215,078	1,523,368
Changes in unrealized gains (losses) included in earnings related to assets still held at end of period	(9,642)	(6,675)	(41,713)	(41,018)
Privately issued commercial [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	17,233	26,643	22,407	25,166
Total gains (losses) realized/ unrealized;
Included in other comprehensive income	1,581	(1,369)	99	4,725
Settlements	(1,985)	(1,794)	(5,677)	(6,411)
Ending Balance	16,829	23,480	16,829	23,480
Collateralized Debt Obligations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	61,601	118,040	110,756	115,346
Total gains (losses) realized/ unrealized;
Included in earnings		(2,857)		(5,703)
Included in other comprehensive income	(9,482)	(5,592)	(2,276)	215
Purchases			50,790
Sales			(105,643)
Settlements	(765)	(249)	(2,273)	(516)
Ending Balance	51,354	109,342	51,354	109,342
Changes in unrealized gains (losses) included in earnings related to assets still held at end of period		(2,857)		(5,703)
Other Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance				420
Total gains (losses) realized/ unrealized;
Included in other comprehensive income				35
Transfer in and/or out of Level 3				$ (455)

Changes in unrealized gains (losses) included in earnings related to assets still held at end of period

Name:	mtb_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetStillHeldGainLossInEarnings
Namespace Prefix:	mtb
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value measurement with unobservable inputs reconciliation recurring basis other asset and other liability still held gain loss in earnings.

+ Details

Name:	mtb_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisOtherAssetAndOtherLiabilityStillHeldGainLossInEarnings
Namespace Prefix:	mtb
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Other Asset And Other Liability Value.

+ Details

Name:	mtb_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisOtherAssetAndOtherLiabilityValue
Namespace Prefix:	mtb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Other Assets and other liabilities Gain Loss Included In Earnings.

+ Details

Name:	mtb_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisOtherAssetsAndOtherLiabilitiesGainLossIncludedInEarnings
Namespace Prefix:	mtb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Other Assets and other liabilities Transfers Net.

+ Details

Name:	mtb_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisOtherAssetsAndOtherLiabilitiesTransfersNet
Namespace Prefix:	mtb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ Details

Name:	us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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.

+ Details

Name:	us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c(1)

-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.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in other comprehensive income (a separate component of shareholders' equity).

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncome
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Purchases that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ 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)(2)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents purchases, sales, issuances, and settlements (net) which have taken place during the period in relation to assets measured at fair value on a recurring basis using unobservable inputs (Level 3).

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchasesSalesIssuancesSettlements
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Sales that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This element represents [net] transfers in to and out of assets measured at fair value on a recurring basis using unobservable inputs (Level 3) which have taken place during the period.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c(3)

-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.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(3)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersNet
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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 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.

Reference 2: 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=6925170&loc=d3e19207-110258

+ Details

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