INTERIM CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (unaudited) shares in Millions, CAD in Millions, $ in Millions	CAD shares	Common shares/Share capital [Member] CAD shares	Common shares/Share capital [Member] USD ($) shares	Additional paid-in capital [Member] CAD	Accumulated other comprehensive loss [Member] CAD	Retained earnings [Member] CAD
Beginning balance (shares) at Dec. 31, 2015 | shares		153.0	153.0
Beginning balance at Dec. 31, 2015	CAD 4,796	CAD 2,058		CAD 43	CAD (1,477)	CAD 4,172
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,215	0		0	0	1,215
Other comprehensive income (loss)	44	0		0	44	0
Dividends declared	(202)	0		0	0	(202)
Effect of stock-based compensation expense	11	CAD 0		11	0	0
CP Common Shares repurchased (shares) | shares		(6.9)	(6.9)
CP Common Shares repurchased (amount)	(1,210)	CAD (84)		0	0	(1,126)
Shares issued under stock option plan (shares) | shares		0.2	0.2
Shares issued under stock option plan	CAD 15	CAD 26		(11)	0	0
Ending balance (shares) at Sep. 30, 2016 | shares	146.3	146.3	146.3
Ending balance at Sep. 30, 2016	CAD 4,669	CAD 2,000		43	(1,433)	4,059
Beginning balance (shares) at Dec. 31, 2016 | shares		146.3	146.3
Beginning balance at Dec. 31, 2016	4,626	CAD 2,002		52	(1,799)	4,371
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,421	0	$ 0	0	0	1,421
Other comprehensive income (loss)	84	0		0	84	0
Dividends declared	(237)	CAD 0		0	0	(237)
CP Common Shares repurchased (shares) | shares		(1.8)	(1.8)
CP Common Shares repurchased (amount)	(368)	CAD (26)		0	0	(342)
Shares issued under stock option plan (shares) | shares		0.5	0.5
Shares issued under stock option plan	CAD 39	CAD 49		(10)	0	0
Ending balance (shares) at Sep. 30, 2017 | shares	145.0	145.0	145.0
Ending balance at Sep. 30, 2017	CAD 5,565	CAD 2,025		CAD 42	CAD (1,715)	CAD 5,213