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Employee Future Benefits - Schedule of Net Benefit Costs (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
DBP Plans    
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]    
Service costs $ 74 $ 62
Interest costs 161 159
Expected return on plan assets (221) (202)
Amortization of actuarial gains (1) (9)
Amortization of past service credits/plan amendments (1) (1)
Regulatory adjustments (1) 12
Net benefit cost 11 21
OPEB Plans    
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]    
Service costs 25 22
Interest costs 29 30
Expected return on plan assets (26) (22)
Amortization of actuarial gains (17) (19)
Amortization of past service credits/plan amendments (1) (1)
Regulatory adjustments 2 5
Net benefit cost $ 12 $ 15