v3.26.1
PENSION PLANS AND POSTRETIREMENT BENEFITS - Changes in the fair value of plan assets (Details) - Plan assets - Pension and postretirement benefits - CAD ($)
$ in Millions
12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Disclosure of net defined benefit liability (asset)    
Fair value of plan assets at the beginning of the year $ 607.0 $ 572.0
Actual return on plan assets 24.0 54.2
Employer contributions 0.6 0.5
Plan participants' contributions 4.7 5.1
Benefits and settlements paid (18.1) (18.3)
Administrative fees (1.2) (1.0)
Transfer (5.2) (5.5)
Fair value of plan assets at the end of the year $ 611.8 $ 607.0