CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - CAD ($) $ in Millions	Total	Share capital	Additional paid-in capital	Accumulated other comprehensive loss	Retained earnings	Cumulative Effect, Period of Adoption, Adjusted Balance	Cumulative Effect, Period of Adoption, Adjusted Balance Retained earnings
Beginning balance at Dec. 31, 2017	$ 6,437	$ 2,032	$ 43	$ (1,741)	$ 6,103
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,951	0	0	0	1,951
Other comprehensive (loss) income	(302)	0	0	(302)	0
Dividends declared	(358)	0	0	0	(358)
Effect of stock-based compensation expense	11	0	11	0	0
CP Common Shares repurchased	(1,127)	(66)	0	0	(1,061)
Shares issued under stock option plan	24	36	(12)	0	0
Ending balance at Dec. 31, 2018	6,636	2,002	42	(2,043)	6,635
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at January 1, as restated		2,002	42	(2,043)		$ 6,631	$ 6,630
Net income	2,440	0	0	0	2,440
Other comprehensive (loss) income	(479)	0	0	(479)	0
Dividends declared	(434)	0	0	0	(434)
Effect of stock-based compensation expense	15	0	15	0	0
CP Common Shares repurchased	(1,140)	(54)	0	0	(1,086)
Shares issued under stock option plan	36	45	(9)	0	0
Ending balance at Dec. 31, 2019	7,069	1,993	48	(2,522)	7,550
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at January 1, as restated		1,993	48	(2,522)		$ 7,068	$ 7,549
Net income	2,444	0	0	0	2,444
Other comprehensive (loss) income	(292)	0	0	(292)	0
Dividends declared	(479)	0	0	0	(479)
Effect of stock-based compensation expense	17	0	17	0	0
CP Common Shares repurchased	(1,477)	(58)	0	0	(1,419)
Shares issued under stock option plan	38	48	(10)	0	0
Ending balance at Dec. 31, 2020	$ 7,319	$ 1,983	$ 55	$ (2,814)	$ 8,095