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	137.0
Beginning balance at Dec. 31, 2019	$ 7,068	$ 1,993	$ 48	$ (2,522)	$ 7,549
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	409	0	0	0	409
Other comprehensive income	42	0	0	42	0
Dividends declared	(112)	0	0	0	(112)
Effect of stock-based compensation expense	$ 5	0	5	0	0
CP Common Shares repurchased (shares)	(1.6)
CP Common Shares repurchased	$ (468)	(21)	0	0	(447)
Shares issued under stock option plan (shares)	0.2
Shares issued under stock option plan	$ 11	13	(2)	0	0
Ending balance (shares) at Mar. 31, 2020	135.6
Ending balance at Mar. 31, 2020	$ 6,955	1,985	51	(2,480)	7,399
Beginning balance (shares) at Dec. 31, 2020	133.3
Beginning balance at Dec. 31, 2020	$ 7,319	1,983	55	(2,814)	8,095
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	602	0	0	0	602
Other comprehensive income	58	0	0	58	0
Dividends declared	(126)	0	0	0	(126)
Effect of stock-based compensation expense	$ 5	0	5	0	0
Shares issued under stock option plan (shares)	0.0
Shares issued under stock option plan	$ 8	10	(2)	0	0
Ending balance (shares) at Mar. 31, 2021	133.3
Ending balance at Mar. 31, 2021	$ 7,866	$ 1,993	$ 58	$ (2,756)	$ 8,571