Shareholders' Equity - Activities Under Share Repurchase Program (Detail) - CAD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2020	Mar. 31, 2019
Common Shares repurchased		1,600,000	700,000
Common Shares repurchased (value)		$ 468	$ 185
Current Normal Course Issuer Bid (NCIB)
Common Shares repurchased	1,750,000	1,455,854
Weighted-average price per share		$ 321.71
Common Shares repurchased (value)	$ 568	$ 468
2018 Normal Course Issuer Bid (NCIB)
Common Shares repurchased			707,678
Weighted-average price per share			$ 261.73
Common Shares repurchased (value)			$ 185