v3.26.1
FINANCIAL RISK MANAGEMENT - Forward Foreign Currency Contracts (Details) - Currencies (sold/bought)
$ in Millions
 12 Months Ended
Mar. 31, 2026
CAD ($)
Mar. 31, 2025
CAD ($)
Disclosure of risk management strategy related to hedge accounting [line items]    
Notional amount $ 2,402.8 $ 2,829.3
USD/CDN | Less than 1 year    
Disclosure of risk management strategy related to hedge accounting [line items]    
Notional amount $ 1,003.6 $ 1,257.8
Average rate (in percent) 0.73 0.72
USD/CDN | Between 1 and 3 years    
Disclosure of risk management strategy related to hedge accounting [line items]    
Notional amount $ 259.7 $ 250.8
Average rate (in percent) 0.74 0.73
USD/CDN | Between 3 and 5 years    
Disclosure of risk management strategy related to hedge accounting [line items]    
Notional amount $ 0.0 $ 0.4
Average rate (in percent) 0 0.75
EUR/CDN | Less than 1 year    
Disclosure of risk management strategy related to hedge accounting [line items]    
Notional amount $ 428.9 $ 308.1
Average rate (in percent) 0.63 0.66
EUR/CDN | Between 1 and 3 years    
Disclosure of risk management strategy related to hedge accounting [line items]    
Notional amount $ 55.1 $ 60.7
Average rate (in percent) 0.64 0.66
EUR/CDN | Between 3 and 5 years    
Disclosure of risk management strategy related to hedge accounting [line items]    
Notional amount $ 0.0 $ 2.4
Average rate (in percent) 0 0.65
CDN/USD | Less than 1 year    
Disclosure of risk management strategy related to hedge accounting [line items]    
Notional amount $ 231.5 $ 489.6
Average rate (in percent) 1.38 1.42
CDN/USD | Between 1 and 3 years    
Disclosure of risk management strategy related to hedge accounting [line items]    
Notional amount $ 2.8 $ 31.3
Average rate (in percent) 1.39 1.39
CDN/USD | Between 3 and 5 years    
Disclosure of risk management strategy related to hedge accounting [line items]    
Notional amount $ 0.0 $ 0.2
Average rate (in percent) 0 1.37
Other currencies | Less than 1 year    
Disclosure of risk management strategy related to hedge accounting [line items]    
Notional amount $ 420.6 $ 426.4
Other currencies | Between 1 and 3 years    
Disclosure of risk management strategy related to hedge accounting [line items]    
Notional amount $ 0.6 $ 1.6