CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - CAD CAD in Millions	Total	Share capital [Member]	Additional paid-in capital [Member]	Accumulated other comprehensive loss [Member]	Retained earnings [Member]
Beginning Balance at Dec. 31, 2014	CAD 5,610	CAD 2,185	CAD 36	CAD (2,219)	CAD 5,608
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,352	0	0	0	1,352
Other comprehensive income (loss)	742	0	0	742	0
Dividends declared	(221)	0	0	0	(221)
Effect of stock-based compensation expense	17	0	17	0	0
CP Common Shares repurchased	(2,748)	(181)	0	0	(2,567)
Stock issued under stock option plan	44	54	(10)	0	0
Ending Balance at Dec. 31, 2015	4,796	2,058	43	(1,477)	4,172
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,599	0	0	0	1,599
Other comprehensive income (loss)	(322)	0	0	(322)	0
Dividends declared	(274)	0	0	0	(274)
Effect of stock-based compensation expense	14	0	14	0	0
CP Common Shares repurchased	(1,210)	(84)	0	0	(1,126)
Stock issued under stock option plan	23	28	(5)	0	0
Ending Balance at Dec. 31, 2016	4,626	2,002	52	(1,799)	4,371
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,405	0	0	0	2,405
Other comprehensive income (loss)	58	0	0	58	0
Dividends declared	(319)	0	0	0	(319)
Effect of stock-based compensation expense	3	0	3	0	0
CP Common Shares repurchased	(381)	(27)	0	0	(354)
Stock issued under stock option plan	45	57	(12)	0	0
Ending Balance at Dec. 31, 2017	CAD 6,437	CAD 2,032	CAD 43	CAD (1,741)	CAD 6,103