Shareholders' Equity - Activities Under Shares Repurchase Program (Detail) - CAD CAD / shares in Units, CAD in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Current Normal Course Issuer Bid (NCIB) [Member]
CP Common Shares repurchased (shares)	682,900		682,900
Weighted-average price per share	CAD 208.75		CAD 208.75
Purchase of CP Common Shares	CAD 143		CAD 143
Normal Course Issuer Bid (NCIB) [Member]
CP Common Shares repurchased (shares)		5,127,800		5,127,800
Weighted-average price per share		CAD 169.13		CAD 169.13
Purchase of CP Common Shares		CAD 867		CAD 867