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		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Earnings Per Share [Abstract]
Net income	$ 1,324	$ 765	$ 2,124	$ 1,355
Weighted-average basic shares outstanding (in shares)	931.2	929.9	930.9	929.8
Dilutive effect of stock options (in shares)	2.6	2.7	2.7	2.9
Weighted-average diluted shares outstanding (in shares)	933.8	932.6	933.6	932.7
Earnings per share - basic (in dollars per share)	$ 1.42	$ 0.82	$ 2.28	$ 1.46
Earnings per share - diluted (in dollars per share)	$ 1.42	$ 0.82	$ 2.28	$ 1.45