Shareholders' Equity - Activities Under Shares Repurchase Program (Detail) - CAD CAD / shares in Units, CAD in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
CP Common Shares repurchased (amount)			CAD 368	CAD 1,210
Current Normal Course Issuer Bid (NCIB) [Member]
CP Common Shares repurchased (shares)	1,145,400		1,828,300
Weighted-average price per share	CAD 196.46		CAD 201.50
CP Common Shares repurchased (amount)	CAD 225		CAD 368
Normal Course Issuer Bid (NCIB) [Member]
CP Common Shares repurchased (shares)		1,782,200		6,910,000
Weighted-average price per share		CAD 192.10		CAD 175.08
CP Common Shares repurchased (amount)		CAD 342		CAD 1,210