Shareholders' Equity - Activities Under Share Repurchase Program (Detail) - CAD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended		8 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019
Common Shares repurchased (shares)	900,000	1,200,000	1,600,000	2,500,000
Common Shares repurchased	$ 296	$ 241	$ 481	$ 559
Current Normal Course Issuer Bid (NCIB) [Member]
Common Shares repurchased (shares)	956,243		1,663,921		3,850,000
Weighted-average price per share	$ 308.84		$ 288.80
Common Shares repurchased	$ 296		$ 481		$ 1,049
2017 Normal Course Issuer Bid (NCIB) [Member]
Common Shares repurchased (shares)		1,060,262		2,495,962
Weighted-average price per share		$ 226.97		$ 223.97
Common Shares repurchased		$ 241		$ 559