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, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Earnings Per Share [Abstract]
Net income attributable to controlling shareholders	$ 1,234	$ 905	$ 2,144	$ 1,680
Weighted-average basic shares outstanding (in shares)	923.8	932.8	928.4	932.6
Dilutive effect of stock options (in shares)	1.0	1.8	1.1	1.9
Weighted-average diluted shares outstanding (in shares)	924.8	934.6	929.5	934.5
Earnings per share - basic (in dollars per share)	$ 1.34	$ 0.97	$ 2.31	$ 1.80
Earnings per share - diluted (in dollars per share)	$ 1.33	$ 0.97	$ 2.31	$ 1.80