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, 2023	Mar. 31, 2022
Earnings Per Share [Abstract]
Net income	$ 800	$ 590
Weighted-average basic shares outstanding (in shares)	930.7	929.7
Dilutive effect of stock options (in shares)	2.8	3.0
Weighted-average diluted shares outstanding (in shares)	933.5	932.7
Basic earnings per share (in dollars per share)	$ 0.86	$ 0.63
Diluted earnings per share (in dollars per share)	$ 0.86	$ 0.63