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Employee Future Benefits - Summary of Components of Net Benefit Cost for Pension Plans and Retiree Welfare Plans (Detail) - Net Benefit Cost Recognized in the Consolidated Statements of Income [Member] - 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 current service cost $ 43 $ 44
Defined benefit administrative expenses 11 9
Past service cost-plan amendments and curtailments (6)  
Service cost 48 53
Interest on net defined benefit (asset) liability 2 6
Defined benefit cost 50 59
Defined contribution cost 85 90
Net benefit cost 135 149
Retiree welfare plans [Member]    
Disclosure of defined benefit plans [Line Items]    
Defined benefit administrative expenses 2 2
Service cost 2 2
Interest on net defined benefit (asset) liability   1
Defined benefit cost 2 3
Net benefit cost $ 2 $ 3