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	1,642	0	0	0	1,642
Other comprehensive income	106	0	0	106	0
Dividends declared	(353)	0	0	0	(353)
Effect of stock-based compensation expense	$ 13	0	13	0	0
CP Common Shares repurchased (shares)	(13.7)
CP Common Shares repurchased	$ (916)	(39)	0	0	(877)
Shares issued under stock option plan (shares)	1.2
Shares issued under stock option plan	$ 19	24	(5)	0	0
Ending balance (shares) at Sep. 30, 2020	672.5
Ending balance at Sep. 30, 2020	$ 7,579	1,978	56	(2,416)	7,961
Beginning balance (shares) at Jun. 30, 2020	677.6
Beginning balance at Jun. 30, 2020	$ 7,465	1,990	53	(2,450)	7,872
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	598	0	0	0	598
Other comprehensive income	34	0	0	34	0
Dividends declared	(128)	0	0	0	(128)
Effect of stock-based compensation expense	$ 4	0	4	0	0
CP Common Shares repurchased (shares)	(5.3)
CP Common Shares repurchased	$ (396)	(15)	0	0	(381)
Shares issued under stock option plan (shares)	0.2
Shares issued under stock option plan	$ 2	3	(1)	0	0
Ending balance (shares) at Sep. 30, 2020	672.5
Ending balance at Sep. 30, 2020	$ 7,579	1,978	56	(2,416)	7,961
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	2,320	0	0	0	2,320
Other comprehensive income	171	0	0	171	0
Dividends declared	(380)	0	0	0	(380)
Effect of stock-based compensation expense	$ 18	0	18	0	0
Shares issued under stock option plan (shares)	0.6
Shares issued under stock option plan	$ 20	25	(5)	0	0
Ending balance (shares) at Sep. 30, 2021	666.9
Ending balance at Sep. 30, 2021	$ 9,468	2,008	68	(2,643)	10,035
Beginning balance (shares) at Jun. 30, 2021	666.8
Beginning balance at Jun. 30, 2021	$ 8,965	2,003	63	(2,791)	9,690
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	472	0	0	0	472
Other comprehensive income	148	0	0	148	0
Dividends declared	(127)	0	0	0	(127)
Effect of stock-based compensation expense	$ 6	0	6	0	0
Shares issued under stock option plan (shares)	0.1
Shares issued under stock option plan	$ 4	5	(1)	0	0
Ending balance (shares) at Sep. 30, 2021	666.9
Ending balance at Sep. 30, 2021	$ 9,468	$ 2,008	$ 68	$ (2,643)	$ 10,035