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Restructuring, acquisition and related integration costs - Narrative (Details) - CAD ($) | 12 Months Ended | 18 Months Ended
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Mar. 31, 2024
Disclosure of attribution of expenses by nature to their function [line items] |  |  |
Restructuring | $ 196,796,000 | $ 0 |
Cost optimization program | 0 | 91,063,000 | $ 100,027,000
Acquisition and related integration costs | 88,235,000 | 5,866,000 |
Professional fees | 268,322,000 | 293,452,000 |
Restructuring |  |  |
Disclosure of attribution of expenses by nature to their function [line items] |  |  |
Termination of employment costs | 190,008,000 |  |
Cost of vacating leased premises | 6,788,000 |  |
Cost optimization program |  |  |
Disclosure of attribution of expenses by nature to their function [line items] |  |  |
Termination of employment costs |  | 69,500,000 |
Cost of vacating leased premises |  | 21,563,000 |
Acquisition and related integration costs |  |  |
Disclosure of attribution of expenses by nature to their function [line items] |  |  |
Termination of employment costs | 27,467,000 | 653,000 |
Cost of vacating leased premises | 23,379,000 | 947,000 |
Professional fees | $ 12,278,000 | $ 2,437,000 |

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