Loans and Leases - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Loans And Leases Receivable [Line Items]
Amount of foreclosed residential real estate property held	$ 24	$ 28
Loans secured by residential real estate that were in the process of foreclosure	$ 151	214
Percentage loans in the process of foreclosure, serviced by other entities, classified as government guaranteed	44.00%
Guaranteed amount included in the estimated residual value of leased assets associated with direct financing leases	$ 29	34
Director and Certain Officers [Member]
Loans And Leases Receivable [Line Items]
Exclusion limit of loans from related party disclosure	less than $60,000
Borrowing by directors and certain officers of M&T and its banking subsidiaries and their associates	$ 113	72
New borrowings by directors, certain officers and their associates	42
Repayments and other reductions of borrowings by directors, certain officers and their associates	1
Commercial Real Estate [Member]
Loans And Leases Receivable [Line Items]
Loans pledged to secure outstanding borrowings from the FHLB of New York	11,900
Residential Mortgage Loans [Member]
Loans And Leases Receivable [Line Items]
Loans pledged to secure outstanding borrowings from the FHLB of New York	11,500
Residential Mortgage Loans [Member] \| One-to-Four Family Residential [Member]
Loans And Leases Receivable [Line Items]
Mortgage loans held for sale	474	777
Commercial Real Estate Loans [Member] \| One-to-Four Family Residential [Member]
Loans And Leases Receivable [Line Items]
Mortgage loans held for sale	425	$ 278
Commercial Loans and Leases [Member]
Loans And Leases Receivable [Line Items]
Loans pledged to secure outstanding borrowings from the FHLB of New York	9,500
Home Equity Loans and Lines of Credit [Member]
Loans And Leases Receivable [Line Items]
Loans pledged to secure outstanding borrowings from the FHLB of New York	1,900
Other Consumer Loans [Member]
Loans And Leases Receivable [Line Items]
Loans pledged to secure outstanding borrowings from the FHLB of New York	$ 10,200

The amount of residual value associated with direct financing leases that are guaranteed by the lessees or others.

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- Definition

Loans and leases receivable.

+ References

No definition available.

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- Definition

Percentage of loans in the process of foreclosure, serviced by other entities, classified as government guaranteed.

+ References

No definition available.

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- Definition

Residential mortgage loans secured by residential real estate in process of foreclosure.

+ References

No definition available.

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- Definition

For an unclassified balance sheet, reflects the carrying amount of unpaid loan amounts due from related parties at the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
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-Subparagraph (SX 210.9-03.7(e))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

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- Definition

Reflects the amount of new advances made to related parties in the form of loan and lease receivables.

+ References

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- Definition

Describes transactions with related parties, including directors, officers and key employees, including: (1) the aggregate amount of related party loans if they exceed 5 percent of shareholders' equity at the balance sheet date or at any time during the latest fiscal year, (2) an analysis of activity with respect to such loans for the latest fiscal year (i.e., beginning balance, new loans, repayments, other changes and ending balance), (3) the aggregate amount of any significant nonaccrual of interest, past due amounts, or restructured or potential problem (including additional information necessary to understand the impact on the financial statements), and (4) any related party loans not made in the ordinary course of business.

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- Definition

Amount of cash inflow from related parties which reduce the amount of loans and leases receivable due from related parties.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7)(e)(1)(i))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3179-108585

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- Definition

Amount, after valuation allowance, of financing receivable held for sale and not part of disposal group. Excludes loan covered under loss sharing agreement and loan classified as investment in debt security.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=124259787&loc=d3e4428-111522

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 310
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124265262&loc=d3e48678-111004

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- Definition

Carrying amount as of the balance sheet date of other real estate and foreclosed assets. Other real estate may include real estate investments, real estate loans that qualify as investments in real estate, and premises that are no longer used in operations may also be included in real estate owned. Foreclosed assets include all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10(4))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

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- Definition

The carrying amount, as of the date of the latest financial statement presented, of loans receivable which are owned but transferred to serve as collateral for the payment of FHLB debt obligations, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
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