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Loans and Allowance for Credit Losses - Summary of Credit Risk Exposures for Loans Carried at Amortized Cost, FVOCI or FVTPL (Parenthetical) (Detail) - CAD ($) $ in Millions | 12 Months Ended
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Oct. 31, 2025 | Oct. 31, 2024
Stage 3 [member] |  |
Disclosure of credit risk exposure [line items] |  |
Percentage of collateralized loan | 94.00% | 92.00%
Credit Card Loans [member] | Principal [member] | Bottom of range [member] |  |
Disclosure of credit risk exposure [line items] |  |
Number of days for which the loan receivable is overdue for the loans to be written off | 180 days | 180 days
Credit Card Loans [member] | Interest [member] | Bottom of range [member] |  |
Disclosure of credit risk exposure [line items] |  |
Number of days for which the loan receivable is overdue for the loans to be written off | 180 days | 180 days
Residential mortgages [member] | FVTPL loans [member] | Stage 1 [member] |  |
Disclosure of credit risk exposure [line items] |  |
FVTPL loans | $ 79 | $ 163
Business and government loans [member] | FVTPL loans [member] | Stage 1 [member] |  |
Disclosure of credit risk exposure [line items] |  |
FVTPL loans | $ 13,231 | $ 12,431

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- Definition Loans and receivables carried at fair value through profit or loss. + References No definition available. + Details
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Period Type: | instant

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- Definition Number of days for which the loan receivable is overdue for the loans to be written off. + References No definition available. + Details
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Namespace Prefix: | bmo_
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- Definition Percentage of collateralized loan. + References No definition available. + Details
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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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- Details
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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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Balance Type: |
Period Type: |

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