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	868	0		0	0	868
Other comprehensive income (loss)	6	0		0	6	0
Dividends declared	(130)	0		0	0	(130)
Effect of stock-based compensation expense	8	CAD 0		8	0	0
CP Common Shares repurchased (shares) | shares		(4.7)	(4.7)
CP Common Shares repurchased	(867)	CAD (70)		0	0	(797)
Shares issued under stock option plan (shares) | shares		0.1	0.1
Shares issued under stock option plan	CAD 10	CAD 12		(2)	0	0
Ending balance (shares) at Jun. 30, 2016 | shares	148.4	148.4	148.4
Ending balance at Jun. 30, 2016	CAD 4,691	CAD 2,000		49	(1,471)	4,113
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	911	0	$ 0	0	0	911
Other comprehensive income (loss)	59	0		0	59	0
Dividends declared	(156)	CAD 0		0	0	(156)
CP Common Shares repurchased (shares) | shares		(0.7)	(0.7)
CP Common Shares repurchased	(143)	CAD (10)		0	0	(133)
Shares issued under stock option plan (shares) | shares		0.5	0.5
Shares issued under stock option plan	CAD 36	CAD 46		(10)	0	0
Ending balance (shares) at Jun. 30, 2017 | shares	146.1	146.1	146.1
Ending balance at Jun. 30, 2017	CAD 5,333	CAD 2,038		CAD 42	CAD (1,740)	CAD 4,993