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, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Earnings Per Share [Abstract]
Net income attributable to controlling shareholders	$ 905	$ 1,324	$ 1,680	$ 2,124
Weighted-average basic shares outstanding (in shares)	932.8	931.2	932.6	930.9
Dilutive effect of stock options (in shares)	1.8	2.6	1.9	2.7
Weighted-average diluted shares outstanding (in shares)	934.6	933.8	934.5	933.6
Earnings per share - basic (in dollars per share)	$ 0.97	$ 1.42	$ 1.80	$ 2.28
Earnings per share - diluted (in dollars per share)	$ 0.97	$ 1.42	$ 1.80	$ 2.28