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IFRS 7 Disclosure - Credit and Counterparty Risk - Additional Information (Detail) - CAD ($) $ in Millions | 12 Months Ended |
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Oct. 31, 2025 | Oct. 31, 2024
Disclosure of credit risk exposure [line items] |  |
Credit assets exposure value | $ 360,814 | $ 353,309
Outstanding credit exposures | 1,189,600 |
Canada [member] |  |
Disclosure of credit risk exposure [line items] |  |
Outstanding credit exposures | 596,400 |
United States [member] |  |
Disclosure of credit risk exposure [line items] |  |
Outstanding credit exposures | 542,700 |
Other Jurisdications [member] |  |
Disclosure of credit risk exposure [line items] |  |
Outstanding credit exposures | $ 50,500 |
Credit risk [member] | Residential real estate loan [member] |  |
Disclosure of credit risk exposure [line items] |  |
Loan to value ratio | 80.00% |

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- Definition Loan to value ratio. + References No definition available. + Details
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Namespace Prefix: | bmo_
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Balance Type: | na
Period Type: | duration

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- Definition Outstanding credit exposures. + References No definition available. + Details
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Namespace Prefix: | bmo_
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Balance Type: | credit
Period Type: | instant

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- Definition Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with members defined in one or many axes of the table. + References No definition available. + Details
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- Definition The maximum exposure to the credit risk of financial assets designated as measured at fair value through profit or loss. [Refer: Credit risk [member]; Maximum exposure to credit risk] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2024-01-01 -Paragraph 9 -Subparagraph a -URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2024-en-r&anchor=para_9_a&doctype=Standard -URIDate 2024-03-27 + Details
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- Details
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Namespace Prefix: |
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |