Shareholders' Equity - Activities Under Share Repurchase Program (Detail) - CAD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019
Number of Common Shares repurchased	100,000	900,000		1,700,000	1,600,000
Amount of repurchase (in millions of Canadian dollars)	$ 52	$ 296		$ 520	$ 481
Current Normal Course Issuer Bid (NCIB)
Number of Common Shares repurchased	150,860		1,900,000	1,606,714
Weighted-average price per share	$ 341.27			$ 323.54
Amount of repurchase (in millions of Canadian dollars)	$ 52		$ 620	$ 520
2018 Normal Course Issuer Bid (NCIB)
Number of Common Shares repurchased		956,243			1,663,921
Weighted-average price per share		$ 308.84			$ 288.80
Amount of repurchase (in millions of Canadian dollars)		$ 296			$ 481