Other Income and Other Expense - Other Income and Other Expense (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other income:
Bank owned life insurance	$ 50,004us-gaap_BankOwnedLifeInsuranceIncome	$ 56,120us-gaap_BankOwnedLifeInsuranceIncome	$ 51,199us-gaap_BankOwnedLifeInsuranceIncome
Credit-related fee income	72,454mtb_CreditRelatedFeeIncome	72,271mtb_CreditRelatedFeeIncome	68,596mtb_CreditRelatedFeeIncome
Letter of credit fees	56,708mtb_LetterOfCreditFees	59,889mtb_LetterOfCreditFees	58,496mtb_LetterOfCreditFees
Gains from loan securitization transactions		63,066mtb_GainsFromSecuritizationActivities
Other expense:
Professional services	401,946us-gaap_ProfessionalFees	335,794us-gaap_ProfessionalFees	248,544us-gaap_ProfessionalFees
Amortization of capitalized servicing rights	68,410	65,354	59,555
Advertising and promotion		$ 56,597us-gaap_MarketingAndAdvertisingExpense	$ 52,388us-gaap_MarketingAndAdvertisingExpense

Credit related fee income.

No definition available.

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- Definition

Gains From Securitization Activities

+ References

No definition available.

+ Details

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- Definition

Letter of credit fees.

+ References

No definition available.

+ Details

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- Definition

The periodic amortization (in proportion to and over the period of estimated net servicing income or loss) of capitalized servicing rights, which contractually entitle the servicer to receive fees and ancillary revenues for performing billing, collection, disbursement and recordkeeping services in connection with a mortgage portfolio. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 4

-Subparagraph (a)(4)

-URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122739-111746

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- Definition

Earnings on or other increases in the value of the cash surrender value of bank owned life insurance policies.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.13)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

+ Details

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- Definition

The total expense recognized in the period for promotion, public relations, and brand or product advertising.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.4)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

+ Details

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- Details

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- Definition

A fee charged for services from professionals such as doctors, lawyers and accountants. The term is often expanded to include other professions, for example, pharmacists charging to maintain a medicinal profile of a client or customer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 946

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.6-07.2(a),(b),(c),(d))

-URI http://asc.fasb.org/extlink&oid=6488393&loc=d3e606610-122999

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 946

-SubTopic 225

-Section 45

-Paragraph 3

-Subparagraph (k)

-URI http://asc.fasb.org/extlink&oid=6488370&loc=d3e13550-115849

+ Details

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