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
	Mar. 31, 2025	Mar. 31, 2024
Earnings Per Share [Abstract]
Net income attributable to controlling shareholders	$ 910	$ 775
Weighted-average basic shares outstanding (in shares)	933.2	932.4
Dilutive effect of stock options (in shares)	1.1	2.0
Weighted-average diluted shares outstanding (in shares)	934.3	934.4
Earnings per share - basic (in dollars per share)	$ 0.98	$ 0.83
Earnings per share - diluted (in dollars per share)	$ 0.97	$ 0.83