Shareholders' Equity - Activities Under Share Repurchase Program (Detail) - CAD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended		11 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019
Number of Common Shares repurchased	1,600,000		3,200,000	2,500,000
Amount of repurchase (in millions)	$ 471		$ 952	$ 559
Current Normal Course Issuer Bid (NCIB) [Member]
Number of Common Shares repurchased	1,519,540		3,183,461		5,370,000
Weighted-average price per share	$ 310.36		$ 299.09
Amount of repurchase (in millions)	$ 471		$ 952		$ 1,520
2017 Normal Course Issuer Bid (NCIB) [Member]
Number of Common Shares repurchased		0		2,495,962
Weighted-average price per share		$ 0		$ 223.97
Amount of repurchase (in millions)		$ 0		$ 559