Fully Benefit-Responsive Investments - Additional Information (Details) - EBP 001 [Member]	12 Months Ended
Dec. 31, 2025
EBP, Fully Benefit-Responsive Investment Contract [Line Items]
EBP, Fully benefit-responsive investment contract, limitation on transacting at contract value, not probable [true false]	true
EBP, Fully benefit-responsive investment contract, termination, description	The investment contracts do not permit the issuers to terminate the agreements prior to the scheduled maturity date.

Indicates (true false) whether event limiting ability to transact fully benefit-responsive investment contract held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) at contract value is not probable of occurring.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 962
-SubTopic 325
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478873/962-325-55-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 325
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477783/962-325-50-3

+ Details

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Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:booleanItemType
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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 325
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477783/962-325-50-3

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 325
-Name Accounting Standards Codification
-Section 45
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477509/962-325-45-5

+ Details

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

- Definition

Description of event and circumstance to allow issuer to terminate fully benefit-responsive investment contract with employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) and settle at amount different from contract value.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 962
-SubTopic 325
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478873/962-325-55-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 325
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477783/962-325-50-3

+ Details

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

- Details

Name:	dei_LegalEntityAxis=bmo_EBP001Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: