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Commitments and contingencies - Commitments and Contingent Liabilities Outstanding (Detail) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Commitments to extend credit
Commercial and industrial	$ 35,781	$ 31,521
Commercial real estate loans to be sold	1,074	479
Other commercial real estate	1,956	2,697
Residential real estate loans to be sold	329	190
Other residential real estate	757	517
Home equity lines of credit	7,906	7,933
Credit cards	6,486	6,087
Other	364	244
Standby letters of credit	2,271	2,260
Commercial letters of credit	75	58
Financial guarantees and indemnification contracts	4,552	4,335
Commitments to sell real estate loans	$ 1,868	$ 1,142

X

- Definition

Commitments regarding commercial letters of credit.

+ References

No definition available.

+ Details

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Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Commitments regarding financial guarantees and indemnification contracts.

+ References

No definition available.

+ Details

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Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Commitments to extend credit.

+ References

No definition available.

+ Details

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Namespace Prefix:	mtb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Commitments To Extend Credit For Commercial And Industrial

+ References

No definition available.

+ Details

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Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Commitments to extend credit for commercial and other.

+ References

No definition available.

+ Details

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Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Commitments to extend credit for commercial real estate loans to be sold.

+ References

No definition available.

+ Details

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Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Commitments To Extend Credit For Credit Cards

+ References

No definition available.

+ Details

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Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Commitments to extend credit for home equity lines of credit.

+ References

No definition available.

+ Details

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Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Commitments to extend credit for other commercial real estate.

+ References

No definition available.

+ Details

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Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Commitments to extend credit for other residential real estate.

+ References

No definition available.

+ Details

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Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Commitments to extend credit for residential real estate loans to be sold.

+ References

No definition available.

+ Details

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Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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- Definition

Commitments to sell real estate loans notional amount.

+ References

No definition available.

+ Details

Name:	mtb_CommitmentsToSellRealEstateLoansNotionalAmount
Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 944
-SubTopic 605
-Name Accounting Standards Codification
-Section 55
-Paragraph 15
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477548/944-605-55-15

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 944
-SubTopic 605
-Name Accounting Standards Codification
-Section 55
-Paragraph 12
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477548/944-605-55-12

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	credit
Period Type:	instant