Stock-Based Compensation - Summary of Activity Related to Employee PSUs (Detail) - Performance Share Unit Plan [Member] $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2022 CAD ($) $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Units, Outstanding as of December 31, 2021 | shares	285
Number of Units, Granted including DRIP | shares	62
Number of Units, Exercised | shares	(123)
Number of Units, Forfeited | shares	(51)
Number of Units, Transferred | shares	3
Number of Units, Outstanding as of December 31, 2022 | shares	176
Weighted Average Grant Date Fair Value, Outstanding as of December 31, 2021 | $ / shares	$ 47.74
Weighted Average Grant Date Fair Value, Granted including DRIP | $ / shares	59.26
Weighted Average Grant Date Fair Value, Exercised | $ / shares	42.86
Weighted Average Grant Date Fair Value, Forfeited | $ / shares	44.41
Weighted Average Grant Date Fair Value, Transferred | $ / shares	47.98
Weighted Average Grant Date Fair Value, Outstanding as of December 31, 2022 | $ / shares	$ 56.21
Aggregate Intrinsic Value, Outstanding as of December 31, 2021 | $	$ 18
Aggregate Intrinsic Value, Granted including DRIP | $	4
Aggregate Intrinsic Value, Exercised | $	7
Aggregate Intrinsic Value, Forfeited | $	3
Aggregate Intrinsic Value, Transferred | $	0
Aggregate Intrinsic Value, Outstanding as of December 31, 2022 | $	$ 9