Earnings per share - Number of Shares Used in the Earnings Per Share Calculations (Details) - CAD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Earnings Per Share [Abstract]
Net income	$ 3,927	$ 3,517	$ 2,852
Weighted-average basic shares outstanding (in shares)	931.3	930.0	679.7
Dilutive effect of stock options (in shares)	2.4	2.9	3.1
Weighted-average diluted shares outstanding (in shares)	933.7	932.9	682.8
Earnings per share – basic (cad per share)	$ 4.22	$ 3.78	$ 4.20
Earnings per share – diluted (cad per share)	$ 4.21	$ 3.77	$ 4.18