INTERIM CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (unaudited) - CAD ($) shares in Millions, $ in Millions	Total	Share capital	Additional paid-in capital	Accumulated other comprehensive loss	Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at January 1, as restated	$ 6,631	$ 2,002	$ 42	$ (2,043)	$ 6,630
Beginning balance (shares) at Dec. 31, 2018	140.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 1,158	0	0	0	1,158
Other comprehensive income	34	0	0	34	0
Dividends declared	(206)	0	0	0	(206)
Effect of stock-based compensation expense	$ 8	0	8	0	0
CP Common Shares repurchased (shares)	(1.6)
CP Common Shares repurchased	$ (481)	(24)	0	0	(457)
Shares issued under stock option plan (shares)	0.2
Shares issued under stock option plan	$ (13)	(18)	(5)	0	0
Ending balance (shares) at Jun. 30, 2019	139.1
Ending balance at Jun. 30, 2019	$ 7,157	1,996	45	(2,009)	7,125
Beginning balance (shares) at Mar. 31, 2019	139.8
Beginning balance at Mar. 31, 2019	$ 6,814	1,997	46	(2,027)	6,798
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	724	0	0	0	724
Other comprehensive income	18	0	0	18	0
Dividends declared	(115)	0	0	0	(115)
Effect of stock-based compensation expense	$ 3	0	3	0	0
CP Common Shares repurchased (shares)	(0.9)
CP Common Shares repurchased	$ (296)	(14)	0	0	(282)
Shares issued under stock option plan (shares)	0.2
Shares issued under stock option plan	$ (9)	(13)	(4)	0	0
Ending balance (shares) at Jun. 30, 2019	139.1
Ending balance at Jun. 30, 2019	$ 7,157	1,996	45	(2,009)	7,125
Beginning balance (shares) at Dec. 31, 2019	137.0
Beginning balance at Dec. 31, 2019	$ 7,069	1,993	48	(2,522)	7,550
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,044	0	0	0	1,044
Other comprehensive income	72	0	0	72	0
Dividends declared	(225)	0	0	0	(225)
Effect of stock-based compensation expense	$ 9	0	9	0	0
CP Common Shares repurchased (shares)	(1.7)
CP Common Shares repurchased	$ (520)	(24)	0	0	(496)
Shares issued under stock option plan (shares)	0.2
Shares issued under stock option plan	$ (17)	(21)	(4)	0	0
Ending balance (shares) at Jun. 30, 2020	135.5
Ending balance at Jun. 30, 2020	$ 7,465	1,990	53	(2,450)	7,872
Beginning balance (shares) at Mar. 31, 2020	135.6
Beginning balance at Mar. 31, 2020	$ 6,955	1,985	51	(2,480)	7,399
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	635	0	0	0	635
Other comprehensive income	30	0	0	30	0
Dividends declared	(113)	0	0	0	(113)
Effect of stock-based compensation expense	$ 4	0	4	0	0
CP Common Shares repurchased (shares)	(0.1)
CP Common Shares repurchased	$ (52)	(3)	0	0	(49)
Shares issued under stock option plan (shares)	0.0
Shares issued under stock option plan	$ (6)	(8)	(2)	0	0
Ending balance (shares) at Jun. 30, 2020	135.5
Ending balance at Jun. 30, 2020	$ 7,465	$ 1,990	$ 53	$ (2,450)	$ 7,872