Shareholders' Equity - Activities Under Shares Repurchase Program (Detail) - CAD ($) $ / shares in Units, $ in Millions	3 Months Ended		5 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019
Common Shares repurchased	$ 185	$ 318
Current Normal Course Issuer Bid (NCIB) [Member]
Common Shares repurchased (shares)	707,678		2,890,000
Weighted-average price per share	$ 261.73
Common Shares repurchased	$ 185		$ 753
2017 Normal Course Issuer Bid (NCIB) [Member]
Common Shares repurchased (shares)		1,435,700
Weighted-average price per share		$ 221.76
Common Shares repurchased		$ 318