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Consolidated Statement of Income (Parenthetical) - CAD ($) $ in Millions | 12 Months Ended
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Oct. 31, 2025 | Oct. 31, 2024
Operating Income Expenses [abstract] |  |
Interest income, calculated using the effective interest rate method | $ 7,136 | $ 7,826

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- Definition Interest income on securities calculated using effective interest rate method. + References No definition available. + Details
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Namespace Prefix: | bmo_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Operating Income Expenses [abstract] + References No definition available. + Details
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Namespace Prefix: | bmo_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration