v3.25.4
PENSION AND POST-RETIREMENT AND POST-EMPLOYMENT BENEFITS - Components of Net Periodic Benefit Costs (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Pension Benefits    
Pension Plans, Postretirement and Other Employee Benefits [Line Items]    
Current service cost $ 146 $ 134
Interest cost 411 401
Expected return on plan assets, net of expenses (663) (603)
Amortization of prior service credit (3) (3)
Amortization of actuarial (gains) losses (15) 14
Net periodic benefit credit (124) (57)
Pension costs capitalized 47 52
Pension Benefits | Defined Benefit Plan, Labor    
Pension Plans, Postretirement and Other Employee Benefits [Line Items]    
Net periodic benefit credit 68 75
Pension Benefits | Charged to results of operations    
Pension Plans, Postretirement and Other Employee Benefits [Line Items]    
Net periodic benefit credit 21 23
Post-Retirement and Post-Employment Benefits    
Pension Plans, Postretirement and Other Employee Benefits [Line Items]    
Current service cost 61 57
Interest cost 80 75
Amortization of prior service credit 10 10
Amortization of actuarial (gains) losses (23) (29)
Net periodic benefit credit 128 113
Pension costs capitalized 42 39
Post-Retirement and Post-Employment Benefits | Defined Benefit Plan, Labor    
Pension Plans, Postretirement and Other Employee Benefits [Line Items]    
Net periodic benefit credit 128 113
Post-Retirement and Post-Employment Benefits | Charged to results of operations    
Pension Plans, Postretirement and Other Employee Benefits [Line Items]    
Net periodic benefit credit $ 86 $ 74