Net Income (Loss) Per Share (Detail) - CAD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net income (loss) per common share - basic
Net income (loss)	$ 516	$ 333
Weighted average number of common shares outstanding (millions of shares)	829.0	847.6
Net income (loss) per common share (dollars)	$ 0.62	$ 0.39
Net income (loss) per common share - diluted
Net income (loss)	$ 516	$ 333
Weighted average number of common shares outstanding (millions of shares)	829.0	847.6
Effect of employee share-based awards (millions of shares)	2.5	2.7
Weighted average number of common shares outstanding, assuming dilution (millions of shares)	831.5	850.3
Net income (loss) per common share (dollars)	$ 0.62	$ 0.39