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Employee Future Benefits - Summary of Amounts Recognized in Consolidated Statements of Financial Position (Detail) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Pension defined benefit plans [member]    
Disclosure of defined benefit plans [Line Items]    
Defined benefit obligation $ 3,794 $ 4,560
Fair value of plan assets 3,722 4,510
Deficit 72 50
Effect of asset limit 48 37
Deficit and net defined benefit liability 120 87
Pension defined benefit plans [member] | Funded [Member]    
Disclosure of defined benefit plans [Line Items]    
Deficit and net defined benefit liability (441) (600)
Pension defined benefit plans [member] | Unfunded [Member]    
Disclosure of defined benefit plans [Line Items]    
Deficit and net defined benefit liability 561 687
Retiree welfare plans [Member]    
Disclosure of defined benefit plans [Line Items]    
Defined benefit obligation 466 584
Fair value of plan assets 523 587
Deficit (57) (3)
Effect of asset limit 0  
Deficit and net defined benefit liability (57) (3)
Retiree welfare plans [Member] | Funded [Member]    
Disclosure of defined benefit plans [Line Items]    
Deficit and net defined benefit liability (168) (154)
Retiree welfare plans [Member] | Unfunded [Member]    
Disclosure of defined benefit plans [Line Items]    
Deficit and net defined benefit liability $ 111 $ 151