Shareholders' Equity - Activities Under Shares Repurchase Program (Detail) - CAD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Common Shares repurchased			$ 559	$ 143
Normal Course Issuer Bid (NCIB) [Member]
Common Shares repurchased (in shares)	1,060,262	682,900	2,495,962	682,900
Weighted-average price per share	$ 226.97	$ 208.75	$ 223.97	$ 208.75
Common Shares repurchased	$ 241	$ 143	$ 559	$ 143