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		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net income (loss) per common share - basic
Net income (loss) (millions of Canadian dollars)		$ 2,479	$ (1,857)	$ 2,200
Weighted average number of common shares outstanding (millions of shares)		711.6	735.3	762.7
Net income (loss) per common share (dollars)		$ 3.48	$ (2.53)	$ 2.88
Net income (loss) per common share - diluted
Net income (loss) (millions of Canadian dollars)		$ 2,479	$ (1,857)	$ 2,200
Weighted average number of common shares outstanding (millions of shares)		711.6	735.3	762.7
Effect of employee share-based awards (millions of shares)	[1]	1.6		2.3
Weighted average number of common shares outstanding, assuming dilution (millions of shares)		713.2	735.3	765.0
Net income (loss) per common share (dollars)		$ 3.48	$ (2.53)	$ 2.88
Dividends per common share - declared (dollars)		$ 1.03	$ 0.88	$ 0.85

[1] For 2020, the Net income (loss) per common share – diluted excludes the effect of 1.9 million employee share-based awards. Share-based awards have the potential to dilute basic earnings per share in the future.