EMPLOYEE BENEFITS OBLIGATIONS - Employee Benefit Obligation (Details) - CAD ($) $ in Millions |
Mar. 31, 2026 |
Mar. 31, 2025 |
Mar. 31, 2024 |
|---|---|---|---|
| Disclosure of defined benefit plans [line items] | |||
| Employee benefits obligations - net | $ 61.6 | $ 122.5 | |
| Employee benefit assets | (44.5) | (11.6) | |
| Employee benefit obligations | 106.1 | 134.1 | |
| Funded plans | |||
| Disclosure of defined benefit plans [line items] | |||
| Employee benefits obligations - net | (44.5) | 13.3 | |
| Funded and unfunded defined benefit pension obligations | Funded plans | |||
| Disclosure of defined benefit plans [line items] | |||
| Employee benefits obligations - net | 591.3 | 599.2 | $ 476.3 |
| Funded and unfunded defined benefit pension obligations | Unfunded plans | |||
| Disclosure of defined benefit plans [line items] | |||
| Employee benefits obligations - net | 106.1 | 109.2 | 98.7 |
| Fair value of plan assets | Funded plans | |||
| Disclosure of defined benefit plans [line items] | |||
| Employee benefits obligations - net | $ (635.8) | $ (585.9) | $ (542.0) |