v3.25.4
POST-EMPLOYMENT BENEFITS - Sensitivity of Key Assumptions (Details) - CAD ($)
$ in Millions
12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Discount rate    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.50% 0.50%
Percentage of reasonably possible decrease in actuarial assumption 0.50% 0.50%
Increase (decrease) in accrued benefit obligation due to reasonably possible increase in actuarial assumption $ (168) $ (174)
Increase (decrease) in accrued benefit obligation due to reasonably possible decrease in actuarial assumption $ 189 $ 197
Rate of future compensation increase    
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 accrued benefit obligation due to reasonably possible increase in actuarial assumption $ 10 $ 12
Increase (decrease) in accrued benefit obligation due to reasonably possible decrease in actuarial assumption $ (10) $ (12)
Mortality rate    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Duration of reasonably possible increase in actuarial assumption 1 year 1 year
Duration of reasonably possible decrease in actuarial assumption 1 year 1 year
Increase (decrease) in accrued benefit obligation due to reasonably possible increase in actuarial assumption $ 36 $ 36
Increase (decrease) in accrued benefit obligation due to reasonably possible decrease in actuarial assumption $ (39) $ (40)