v3.26.1
EMPLOYEE BENEFITS OBLIGATIONS - Movement In Defined Benefit Pension Obligation (Details) - CAD ($)
$ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Disclosure of net defined benefit liability (asset) [line items]    
Net defined benefit liability (asset), beginning of year $ 122.5  
Actuarial (gain) loss arising from:    
Net defined benefit liability (asset), end of year 61.6 $ 122.5
Funded plans    
Disclosure of net defined benefit liability (asset) [line items]    
Net defined benefit liability (asset), beginning of year 13.3  
Current service cost 34.5 32.9
Interest cost (25.5) (26.4)
Actuarial (gain) loss arising from:    
Net defined benefit liability (asset), end of year (44.5) 13.3
Funded plans | Present value of defined benefit obligation    
Disclosure of net defined benefit liability (asset) [line items]    
Net defined benefit liability (asset), beginning of year 599.2 476.3
Current service cost 34.5 32.9
Interest cost 26.0 22.7
Actuarial (gain) loss arising from:    
Experience adjustments 0.6 43.4
Economic assumptions (66.0) 23.2
Employee contributions 8.3 12.9
Pension benefits paid (11.3) (12.6)
Foreign currency exchange differences 0.0 (0.4)
Net defined benefit liability (asset), end of year 591.3 599.2
Funded plans | Fair value of plan assets    
Disclosure of net defined benefit liability (asset) [line items]    
Net defined benefit liability (asset), beginning of year (585.9) (542.0)
Interest cost (25.5) (26.4)
Actuarial (gain) loss arising from:    
Return on plan assets, excluding amounts included in interest income 6.1 14.2
Employer contributions 22.3 1.8
Employee contributions (8.3) (12.9)
Pension benefits paid 11.3 12.6
Settlements 0.0 (1.4)
Administrative costs (0.9) (0.8)
Foreign currency exchange differences (0.1) 0.6
Net defined benefit liability (asset), end of year (635.8) (585.9)
Unfunded plans    
Disclosure of net defined benefit liability (asset) [line items]    
Current service cost 3.5 4.8
Interest cost 4.3 4.4
Unfunded plans | Present value of defined benefit obligation    
Disclosure of net defined benefit liability (asset) [line items]    
Net defined benefit liability (asset), beginning of year 109.2 98.7
Current service cost 3.5 4.8
Interest cost 4.3 4.4
Past service cost 0.8 2.4
Actuarial (gain) loss arising from:    
Experience adjustments (2.5) (1.2)
Economic assumptions (5.3) 3.1
Pension benefits paid (4.1) (3.8)
Foreign currency exchange differences (0.2) (0.8)
Net defined benefit liability (asset), end of year 106.1 109.2
Canadian | Funded plans    
Disclosure of net defined benefit liability (asset) [line items]    
Current service cost 34.5 32.9
Interest cost (25.1) (26.0)
Canadian | Funded plans | Present value of defined benefit obligation    
Disclosure of net defined benefit liability (asset) [line items]    
Net defined benefit liability (asset), beginning of year 593.8 471.3
Current service cost 34.5 32.9
Interest cost 25.7 22.4
Actuarial (gain) loss arising from:    
Experience adjustments 0.6 43.3
Economic assumptions (66.0) 23.3
Employee contributions 8.3 12.9
Pension benefits paid (10.9) (12.3)
Foreign currency exchange differences 0.0 0.0
Net defined benefit liability (asset), end of year 586.0 593.8
Canadian | Funded plans | Fair value of plan assets    
Disclosure of net defined benefit liability (asset) [line items]    
Net defined benefit liability (asset), beginning of year (578.3) (535.0)
Interest cost (25.1) (26.0)
Actuarial (gain) loss arising from:    
Return on plan assets, excluding amounts included in interest income 6.1 14.3
Employer contributions 22.3 1.8
Employee contributions (8.3) (12.9)
Pension benefits paid 10.9 12.3
Settlements 0.0 (1.4)
Administrative costs (0.9) (0.8)
Foreign currency exchange differences 0.0 0.0
Net defined benefit liability (asset), end of year (628.3) (578.3)
Canadian | Unfunded plans    
Disclosure of net defined benefit liability (asset) [line items]    
Current service cost 3.1 4.1
Interest cost 4.0 4.0
Canadian | Unfunded plans | Present value of defined benefit obligation    
Disclosure of net defined benefit liability (asset) [line items]    
Net defined benefit liability (asset), beginning of year 97.4 86.2
Current service cost 3.1 4.1
Interest cost 4.0 4.0
Past service cost 0.0 3.6
Actuarial (gain) loss arising from:    
Experience adjustments (2.5) (0.2)
Economic assumptions (4.7) 2.8
Pension benefits paid (3.3) (3.1)
Foreign currency exchange differences 0.0 0.0
Net defined benefit liability (asset), end of year 94.0 97.4
Foreign | Funded plans    
Disclosure of net defined benefit liability (asset) [line items]    
Current service cost 0.0 0.0
Interest cost (0.4) (0.4)
Foreign | Funded plans | Present value of defined benefit obligation    
Disclosure of net defined benefit liability (asset) [line items]    
Net defined benefit liability (asset), beginning of year 5.4 5.0
Current service cost 0.0 0.0
Interest cost 0.3 0.3
Actuarial (gain) loss arising from:    
Experience adjustments 0.0 0.1
Economic assumptions 0.0 (0.1)
Employee contributions 0.0 0.0
Pension benefits paid (0.4) (0.3)
Foreign currency exchange differences 0.0 (0.4)
Net defined benefit liability (asset), end of year 5.3 5.4
Foreign | Funded plans | Fair value of plan assets    
Disclosure of net defined benefit liability (asset) [line items]    
Net defined benefit liability (asset), beginning of year (7.6) (7.0)
Interest cost (0.4) (0.4)
Actuarial (gain) loss arising from:    
Return on plan assets, excluding amounts included in interest income 0.0 (0.1)
Employer contributions 0.0 0.0
Employee contributions 0.0 0.0
Pension benefits paid 0.4 0.3
Settlements 0.0 0.0
Administrative costs 0.0 0.0
Foreign currency exchange differences (0.1) 0.6
Net defined benefit liability (asset), end of year (7.5) (7.6)
Foreign | Unfunded plans    
Disclosure of net defined benefit liability (asset) [line items]    
Current service cost 0.4 0.7
Interest cost 0.3 0.4
Foreign | Unfunded plans | Present value of defined benefit obligation    
Disclosure of net defined benefit liability (asset) [line items]    
Net defined benefit liability (asset), beginning of year 11.8 12.5
Current service cost 0.4 0.7
Interest cost 0.3 0.4
Past service cost 0.8 (1.2)
Actuarial (gain) loss arising from:    
Experience adjustments 0.0 (1.0)
Economic assumptions (0.6) 0.3
Pension benefits paid (0.8) (0.7)
Foreign currency exchange differences (0.2) (0.8)
Net defined benefit liability (asset), end of year $ 12.1 $ 11.8