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		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Earnings Per Share [Abstract]
Net income	$ 780	$ 891	$ 2,904	$ 2,246
Weighted-average basic shares outstanding (in shares)	931.5	930.0	931.1	929.9
Dilutive effect of stock options (in shares)	2.4	2.9	2.6	2.9
Weighted-average diluted shares outstanding (in shares)	933.9	932.9	933.7	932.8
Earnings per share - basic (in dollars per share)	$ 0.84	$ 0.96	$ 3.12	$ 2.42
Earnings per share - diluted (in dollars per share)	$ 0.84	$ 0.96	$ 3.11	$ 2.41