Earnings per share - Number Of Shares Used In the Earnings Per Share Calculations (Details) - CAD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Earnings Per Share [Abstract]
Net income	$ 3,517	$ 2,852	$ 2,444
Weighted-average basic shares outstanding (in shares)	930.0	679.7	677.2
Dilutive effect of weighted average number of stock options (in shares)	2.9	3.1	2.7
Weighted-average diluted shares outstanding (in shares)	932.9	682.8	679.9
Earnings per share - basic (cad per share)	$ 3.78	$ 4.20	$ 3.61
Earnings per share - diluted (cad per share)	$ 3.77	$ 4.18	$ 3.59