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Cash compensation which is paid under incentive compensation plan.

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Maximum period of credited service considered to apply excess of covered compensation for each year of credited service.

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Minimum age for eligibility for coverage under self-insure health care plan, before amendment.

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Refers to the number of branches acquired during the period.

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Refers to the number of consecutive months for which loans remain current before non-accrual loans are returned to accrual status.

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No definition available.

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Refers consecutive period considered in final average compensation.

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Refers to the number of most recent years of actual loss history used in determining historical loss experience for all other unclassified loans.

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No definition available.

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Refers to the percentage of average monthly compensation in excess of covered compensation for each year of credited service.

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No definition available.

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Refers to the period of delinquency after which a loan is placed on non-accrual status.

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No definition available.

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Percentage of premium contribution made under self-insure health care plan.

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Eligible age of current and future retirees to be continued under coverage of plan.

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No definition available.

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Percentage of premium to be paid by retiree under self-insure health care plan.

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Refers to the rolling historical period of net losses used in evaluating general component of valuation allowance for loans not impaired but classified as substandard and special mention.

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Number of trading days considered in valuing common stock .

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The carrying amount of assets an investment adviser manages on behalf of investors.

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Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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

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-Name Accounting Standards Codification

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Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

-Publisher FASB

-Name Accounting Standards Codification

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Percentage of vesting of share-based compensation awards.

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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $)	12 Months Ended	1 Months Ended
	Dec. 31, 2014 Segment	Mar. 31, 2008 Branch	Nov. 30, 2013 Branch	Dec. 31, 2013
LOANS [Abstract]
Period of delinquency after which a loan is placed on non-accrual status	90 days
Number of consecutive months for which loans remain current before non-accrual loans are returned to accrual status	6 months
Rolling historical period of net losses used in evaluating general component of valuation allowance for loans not impaired but classified as substandard and special mention	5 years
Number of most recent years of actual loss history used in determining historical loss experience for all other unclassified loans	2 years
WEALTH MANAGEMENT GROUP FEE INCOME [Abstract]
Unaudited market value of trust assets under administration	$ 1,956,000,000			$ 1,888,000,000
Segment Reporting [Abstract]
Number of operating segments	2us-gaap_NumberOfOperatingSegments
M&T Bank Branch Offices [Member]
Intangible Assets [Abstract]
Number of branches acquired		3
Intangible assets acquired	21,000
Partners Trust Bank [Member] \| Trust Business [Member]
Intangible Assets [Abstract]
Intangible assets acquired	2,400,000
Expected useful life	15 years
Canton Bancorp, Inc. [Member]
Intangible Assets [Abstract]
Intangible assets acquired	8,000
Fort Orange Financial Corp [Member]
Intangible Assets [Abstract]
Intangible assets acquired	1,100,000
Expected useful life	10 years
Bank of America Branch Offices [Member]
Intangible Assets [Abstract]
Number of branches acquired			6
Intangible assets acquired	1,600,000
Bank of America Branch Offices [Member] \| Core Deposit Intangibles [Member]
Intangible Assets [Abstract]
Expected useful life	7 years
MT Branch Offices and Canton Bancorp, Inc. Member] [Member] \| Core Deposit Intangibles [Member]
Intangible Assets [Abstract]
Expected useful life	7 years 3 months
MT Branch Offices and Canton Bancorp, Inc. Member] [Member] \| Customer Relationship Intangibles [Member]
Intangible Assets [Abstract]
Expected useful life	7 years 3 months
Non-qualified Deferred Compensation Plan [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Maximum annual installments period	10 years
Directors' Compensation Plan [Member] \| Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized per calendar year (in shares)	20,000
Required service period	12 months
Trading days period	30 days
Incentive Compensation Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized per calendar year (in shares)	10,000
Cash compensation	$ 300,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized per calendar year (in shares)	15,000
Age limit for forfeiture of stock award	65 years
Restricted Stock [Member] \| Awards Vesting Each Year Commencing with First Anniversary Date of Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage (in hundredths)	20.00%
Restricted Stock [Member] \| Awards Vesting on Fifth Anniversary Date [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage (in hundredths)	100.00%
Defined Contribution Profit Sharing, Savings and Investment Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Number of annual service hours required for eligibility (in hours)	1000 hours
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Normal retirement benefit as percentage of final average compensation (in hundredths)	1.20%
Number of consecutive years considered in final average compensation	5 years
Number of prior years considered in final average compensation	10 years
Maximum service period	25 years
Normal retirement additional benefit (in hundredths)	1.00%
Maximum additional service years	10 years
Percentage of average monthly compensation in excess of covered compensation for each year of credited service (in hundredths)	0.65%
Maximum period of credited service	35 years
Covered compensation period	35 years
Defined Benefit Health Care Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Minimum eligible age	55 years
Contribution percentage (in hundredths)	40.00%
Retiree premium percentage (in hundredths)	100.00%
Cost of coverage contribution (in hundredths)	50.00%
Contribution percentage after amendment (in hundredths)	50.00%
Contribution cost percentage (in hundredths)	50.00%
Minimum [Member] \| Defined Benefit Health Care Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Retiree age group range	55 years
Maximum [Member] \| Defined Benefit Health Care Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Retiree age group range	65 years
Buildings [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	15 years
Buildings [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	50 years
Equipment and Furniture [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Equipment and Furniture [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	10 years