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, 2021	Mar. 31, 2020
Net income (loss) per common share - basic
Net income (loss) (millions of Canadian dollars)		$ 392	$ (188)
Weighted average number of common shares outstanding (millions of shares)		734.1	738.9
Net income (loss) per common share (dollars)		$ 0.53	$ (0.25)
Net income (loss) per common share - diluted
Net income (loss) (millions of Canadian dollars)		$ 392	$ (188)
Weighted average number of common shares outstanding (millions of shares)		734.1	738.9
Effect of employee share-based awards (millions of shares)	[1]	1.6	0.0
Weighted average number of common shares outstanding, assuming dilution (millions of shares)		735.7	738.9
Net income (loss) per common share (dollars)		$ 0.53	$ (0.25)
Dividends per common share - declared (dollars)		$ 0.22	$ 0.22

[1] For three months to March 31, 2020, the Net income (loss) per common share – diluted excludes the effect of 2.0 million employee share-based awards. Share-based awards have the potential to dilute basic earnings per share in the future.