v3.25.4
Employee Future Benefits - Amounts Recognized in Consolidated Statements of Financial Position (Detail) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Pension plans    
Disclosure of defined benefit plans [line items]    
Defined benefit obligation $ 3,602 $ 3,826
Fair value of plan assets 3,643 3,820
Deficit (surplus) (41) 6
Effect of asset limit 46 44
Deficit (surplus) and net defined benefit liability (asset) 5 50
Pension plans | Funded or partially funded plans    
Disclosure of defined benefit plans [line items]    
Deficit (surplus) and net defined benefit liability (asset) (488) (483)
Pension plans | Unfunded plans    
Disclosure of defined benefit plans [line items]    
Deficit (surplus) and net defined benefit liability (asset) 493 533
Retiree welfare plans    
Disclosure of defined benefit plans [line items]    
Defined benefit obligation 379 428
Fair value of plan assets 545 553
Deficit (surplus) (166) (125)
Effect of asset limit 0 0
Deficit (surplus) and net defined benefit liability (asset) (166) (125)
Retiree welfare plans | Funded or partially funded plans    
Disclosure of defined benefit plans [line items]    
Deficit (surplus) and net defined benefit liability (asset) (259) (221)
Retiree welfare plans | Unfunded plans    
Disclosure of defined benefit plans [line items]    
Deficit (surplus) and net defined benefit liability (asset) $ 93 $ 96