v3.25.4
PENSION AND POST-RETIREMENT AND POST-EMPLOYMENT BENEFITS - Summary of Change in Projected Benefit Obligation and Change in Plan Assets (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Change in plan assets    
Employer contributions $ 68 $ 75
Pension Benefits    
Change in PBO    
PBO, beginning of year 8,686 8,665
Current service cost 146 134
Employee contributions 81 74
Interest cost 411 401
Benefits paid (457) (427)
Net actuarial loss (gain) 40 (161)
PBO, end of year 8,907 8,686
Change in plan assets    
Fair value of plan assets, beginning of year 9,333 8,764
Actual return on plan assets 513 869
Benefits paid (457) (427)
Employer contributions 68 75
Employee contributions 81 74
Administrative expenses (21) (22)
Fair value of plan assets, end of year 9,517 9,333
(Funded) unfunded status (610) (647)
Post-Retirement and Post-Employment Benefits    
Change in PBO    
PBO, beginning of year 1,666 1,603
Current service cost 61 57
Employee contributions 0 0
Interest cost 80 75
Benefits paid (76) (71)
Net actuarial loss (gain) 19 2
PBO, end of year 1,750 1,666
Change in plan assets    
Fair value of plan assets, beginning of year 0 0
Actual return on plan assets 0 0
Benefits paid (76) (71)
Employer contributions 76 71
Employee contributions 0 0
Administrative expenses 0 0
Fair value of plan assets, end of year 0 0
(Funded) unfunded status $ 1,750 $ 1,666