Earnings per share - Schedule of Shares Used in the Earnings Per Share Calculations (Details) - CAD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Earnings Per Share [Abstract]
Net income	$ 775	$ 800
Weighted-average basic shares outstanding (in shares)	932.4	930.7
Dilutive effect of stock options (in shares)	2.0	2.8
Weighted-average diluted shares outstanding (in shares)	934.4	933.5
Earnings per share - basic (in dollars per share)	$ 0.83	$ 0.86
Earnings per share - diluted (in dollars per share)	$ 0.83	$ 0.86