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, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Earnings Per Share [Abstract]
Net income attributable to controlling shareholders	$ 837	$ 780	$ 2,517	$ 2,904
Weighted-average basic shares outstanding (in shares)	933.2	931.5	932.8	931.1
Dilutive effect of stock options (in shares)	2.1	2.4	2.0	2.6
Weighted-average diluted shares outstanding (in shares)	935.3	933.9	934.8	933.7
Earnings per share - basic (in dollars per share)	$ 0.90	$ 0.84	$ 2.70	$ 3.12
Earnings per share - diluted (in dollars per share)	$ 0.90	$ 0.84	$ 2.69	$ 3.11