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
Beginning balance (shares) at Dec. 31, 2019	685.0
Beginning balance at Dec. 31, 2019	$ 7,068	$ 1,993	$ 48	$ (2,522)	$ 7,549
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,044	0	0	0	1,044
Other comprehensive (loss) 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)	(8.4)
CP Common Shares repurchased	$ (520)	(24)	0	0	(496)
Shares issued under stock option plan (shares)	1.0
Shares issued under stock option plan	$ 17	21	(4)	0	0
Ending balance (shares) at Jun. 30, 2020	677.6
Ending balance at Jun. 30, 2020	$ 7,465	1,990	53	(2,450)	7,872
Beginning balance (shares) at Mar. 31, 2020	678.1
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 (loss) 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)	(0.7)
CP Common Shares repurchased	$ (52)	(3)	0	0	(49)
Shares issued under stock option plan (shares)	0.2
Shares issued under stock option plan	$ 6	8	(2)	0	0
Ending balance (shares) at Jun. 30, 2020	677.6
Ending balance at Jun. 30, 2020	$ 7,465	1,990	53	(2,450)	7,872
Beginning balance (shares) at Dec. 31, 2020	666.3
Beginning balance at Dec. 31, 2020	$ 7,319	1,983	55	(2,814)	8,095
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,848	0	0	0	1,848
Other comprehensive (loss) income	23	0	0	23	0
Dividends declared	(253)	0	0	0	(253)
Effect of stock-based compensation expense	$ 12	0	12	0	0
Shares issued under stock option plan (shares)	0.5
Shares issued under stock option plan	$ 16	20	(4)	0	0
Ending balance (shares) at Jun. 30, 2021	666.8
Ending balance at Jun. 30, 2021	$ 8,965	2,003	63	(2,791)	9,690
Beginning balance (shares) at Mar. 31, 2021	666.6
Beginning balance at Mar. 31, 2021	$ 7,866	1,993	58	(2,756)	8,571
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,246	0	0	0	1,246
Other comprehensive (loss) income	(35)	0	0	(35)	0
Dividends declared	(127)	0	0	0	(127)
Effect of stock-based compensation expense	$ 7	0	7	0	0
Shares issued under stock option plan (shares)	0.2
Shares issued under stock option plan	$ 8	10	(2)	0	0
Ending balance (shares) at Jun. 30, 2021	666.8
Ending balance at Jun. 30, 2021	$ 8,965	$ 2,003	$ 63	$ (2,791)	$ 9,690