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, 2024	Dec. 31, 2023	Dec. 31, 2022
Earnings Per Share [Abstract]
Net income	$ 3,718	$ 3,927	$ 3,517
Weighted-average basic shares outstanding (in shares)	933.0	931.3	930.0
Dilutive effect of stock options (in shares)	1.6	2.4	2.9
Weighted-average diluted shares outstanding (in shares)	934.6	933.7	932.9
Earnings per share – basic (cad per share)	$ 3.98	$ 4.22	$ 3.78
Earnings per share – diluted (cad per share)	$ 3.98	$ 4.21	$ 3.77