Common shares - Calculation of basic and diluted earnings per common share and the dividend declared by the company on its outstanding common shares (Detail) - CAD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Net income (loss) per common share – basic
Net income (loss)	$ 1,195	$ 1,248
Weighted-average number of common shares outstanding (millions of shares)	535.8	584.2
Net income (loss) per common share (dollars)	$ 2.23	$ 2.14
Net income (loss) per common share – diluted
Net income (loss)	$ 1,195	$ 1,248
Weighted-average number of common shares outstanding (millions of shares)	535.8	584.2
Effect of employee share-based awards (millions of shares)	1.1	1.2
Weighted-average number of common shares outstanding, assuming dilution (millions of shares)	536.9	585.4
Net income (loss) per common share (dollars)	$ 2.23	$ 2.13
Dividends per common share – declared (dollars)	$ 0.60	$ 0.44