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Employee benefits - Sensitivity analysis for actuarial assumptions (Details) - CAD ($) $ in Thousands | 12 Months Ended
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Sep. 30, 2025 | Sep. 30, 2024
Actuarial assumption of discount rates | U.K. |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Percentage of reasonably possible increase in actuarial assumption | 0.25% | 0.25%
Percentage of reasonably possible decrease in actuarial assumption | 0.25% | 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption | $ (15,218) | $ (18,334)
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption | $ 15,941 | $ 19,263
Actuarial assumption of discount rates | France |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Percentage of reasonably possible increase in actuarial assumption | 0.25% | 0.25%
Percentage of reasonably possible decrease in actuarial assumption | 0.25% | 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption | $ (2,819) | $ (2,927)
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption | $ 2,937 | $ 3,056
Actuarial assumption of discount rates | GERMANY |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Percentage of reasonably possible increase in actuarial assumption | 0.25% | 0.25%
Percentage of reasonably possible decrease in actuarial assumption | 0.25% | 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption | $ (1,725) | $ (1,796)
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption | $ 1,795 | $ 1,874
Actuarial assumption of expected rates of salary increases | U.K. |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Percentage of reasonably possible increase in actuarial assumption | 0.25% | 0.25%
Percentage of reasonably possible decrease in actuarial assumption | 0.25% | 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption | $ 88 | $ 181
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption | $ (88) | $ (179)
Actuarial assumption of expected rates of salary increases | France |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Percentage of reasonably possible increase in actuarial assumption | 0.25% | 0.25%
Percentage of reasonably possible decrease in actuarial assumption | 0.25% | 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption | $ 3,040 | $ 3,151
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption | $ (2,929) | $ (3,029)
Actuarial assumption of expected rates of salary increases | GERMANY |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Percentage of reasonably possible increase in actuarial assumption | 0.25% | 0.25%
Percentage of reasonably possible decrease in actuarial assumption | 0.25% | 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption | $ 20 | $ 23
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption | $ (18) | $ (21)
Actuarial assumption of expected rates of pension increases | U.K. |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Percentage of reasonably possible increase in actuarial assumption | 0.25% | 0.25%
Percentage of reasonably possible decrease in actuarial assumption | 0.25% | 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption | $ 9,573 | $ 10,675
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption | $ (8,329) | $ (9,287)
Actuarial assumption of expected rates of pension increases | France |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Percentage of reasonably possible increase in actuarial assumption | 0.25% | 0.25%
Percentage of reasonably possible decrease in actuarial assumption | 0.25% | 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption | $ 0 | $ 0
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption | $ 0 | $ 0
Actuarial assumption of expected rates of pension increases | GERMANY |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Percentage of reasonably possible increase in actuarial assumption | 0.25% | 0.25%
Percentage of reasonably possible decrease in actuarial assumption | 0.25% | 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption | $ 924 | $ 948
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption | $ (893) | $ (913)
Actuarial assumption of expected rates of inflation | U.K. |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Percentage of reasonably possible increase in actuarial assumption | 0.25% | 0.25%
Percentage of reasonably possible decrease in actuarial assumption | 0.25% | 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption | $ 10,803 | $ 12,047
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption | $ (10,577) | $ (11,798)
Actuarial assumption of expected rates of inflation | France |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Percentage of reasonably possible increase in actuarial assumption | 0.25% | 0.25%
Percentage of reasonably possible decrease in actuarial assumption | 0.25% | 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption | $ 3,040 | $ 3,151
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption | $ (2,929) | $ (3,029)
Actuarial assumption of expected rates of inflation | GERMANY |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Percentage of reasonably possible increase in actuarial assumption | 0.25% | 0.25%
Percentage of reasonably possible decrease in actuarial assumption | 0.25% | 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption | $ 924 | $ 948
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption | $ (893) | $ (913)
Actuarial assumption of life expectancy after retirement | U.K. |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Period of reasonably possible increase in actuarial assumption | 1 year | 1 year
Period of reasonably possible decrease in actuarial assumption | 1 year | 1 year
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption | $ 13,356 | $ 15,309
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption | $ (13,750) | $ (15,478)
Actuarial assumption of life expectancy after retirement | France |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Period of reasonably possible increase in actuarial assumption | 1 year | 1 year
Period of reasonably possible decrease in actuarial assumption | 1 year | 1 year
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption | $ 686 | $ 664
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption | $ (733) | $ (710)
Actuarial assumption of life expectancy after retirement | GERMANY |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Period of reasonably possible increase in actuarial assumption | 1 year | 1 year
Period of reasonably possible decrease in actuarial assumption | 1 year | 1 year
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption | $ 2,044 | $ 2,025
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption | $ (1,828) | $ (1,809)

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