Shareholders' Equity - Activities Under Shares Repurchase Program (Detail) - CAD ($) $ / shares in Units, $ in Millions	3 Months Ended		11 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018
Common Shares repurchased	$ 318
Current Normal Course Issuer Bid (NCIB) [Member]
Common Shares repurchased (in shares)	1,435,700		3,300,000
Weighted-average price per share	$ 221.76
Common Shares repurchased	$ 318		$ 699
Normal Course Issuer Bid (NCIB) [Member]
Common Shares repurchased (in shares)		0
Weighted-average price per share		$ 0
Common Shares repurchased		$ 0