v3.26.1
PENSION PLANS AND POSTRETIREMENT BENEFITS - Components of plan assets and reconciliation of funded status (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Disclosure of net defined benefit liability (asset)    
Weighted average duration of defined benefit obligations 15 years 17 years 3 months 18 days
Expected future benefit payments in 2026 $ 18.0  
Reconciliation of funded status to net amount recognized    
Net liability recognized 15.2 $ 17.5
Net liability recognized in other liabilities 16.8 19.3
Net liability recognized in other assets 1.6 1.8
Pension and postretirement benefits    
Reconciliation of funded status to net amount recognized    
Benefit obligations (559.2) (560.8)
Fair value of plan assets 611.8 607.0
Plan surplus 52.6 46.2
Asset limit and minimum funding adjustment (67.8) (63.7)
Net amount recognized $ (15.2) $ (17.5)
Plan assets    
Plan assets    
Debt securities (as a percent) 49.70% 36.20%
Other (as a percent) 18.10% 16.70%
Total plan assets (in percent) 100.00% 100.00%
Plan assets | Canadian    
Plan assets    
Equity securities (as a percent) 12.80% 18.90%
Plan assets | Foreign    
Plan assets    
Equity securities (as a percent) 19.40% 28.20%