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IFRS 7 Disclosure - Market Risk - Structural Balance Sheet Interest Rate Sensitivity (Detail) - CAD ($) $ in Millions | Oct. 31, 2025 | Oct. 31, 2024
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Hundred basis point increase [member] |  |
Market Risk [Line Items] |  |
Pre tax economic value sensitivity | $ (1,736) | $ (1,483)
Pre tax earnings sensitivity over the next twelve month | 357 | 367
Hundred basis point increase [member] | Canada [member] |  |
Market Risk [Line Items] |  |
Pre tax economic value sensitivity | (986) |
Pre tax earnings sensitivity over the next twelve month | 104 |
Hundred basis point increase [member] | United States [member] |  |
Market Risk [Line Items] |  |
Pre tax economic value sensitivity | (750) |
Pre tax earnings sensitivity over the next twelve month | 252 |
Hundred basis point decrease [member] |  |
Market Risk [Line Items] |  |
Pre tax economic value sensitivity | 1,063 | 660
Pre tax earnings sensitivity over the next twelve month | (322) | $ (210)
Hundred basis point decrease [member] | Canada [member] |  |
Market Risk [Line Items] |  |
Pre tax economic value sensitivity | 983 |
Pre tax earnings sensitivity over the next twelve month | (26) |
Hundred basis point decrease [member] | United States [member] |  |
Market Risk [Line Items] |  |
Pre tax economic value sensitivity | 80 |
Pre tax earnings sensitivity over the next twelve month | $ (296) |

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- Definition Market Risk [Line Items] + References No definition available. + Details
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Data Type: | xbrli:stringItemType
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- Definition Pre- tax earnings sensitivity over the next twelve month. + References No definition available. + Details
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Namespace Prefix: | bmo_
Data Type: | xbrli:monetaryItemType
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- Definition Pre- tax economic value sensitivity. + References No definition available. + Details
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Namespace Prefix: | bmo_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
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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: |
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Period Type: |

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