Shareholders' Equity - Activities Under Share Repurchase Program (Detail) - CAD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 19, 2020
Number of Common Shares repurchased		700,000		8,400,000
Amount of repurchase (in millions of Canadian dollars)		$ 52		$ 520
2021 Normal Course Issuer Bid (NCIB)
Number of Common Shares repurchased	0		0
Weighted-average price per share	$ 0		$ 0
Amount of repurchase (in millions of Canadian dollars)	$ 0		$ 0
2019 Normal Course Issuer Bid (NCIB)
Number of Common Shares repurchased		754,300		8,033,570	21,400,000
Weighted-average price per share		$ 68.25		$ 64.71
Amount of repurchase (in millions of Canadian dollars)		$ 52		$ 520	$ 1,577