Investment in KCS - Summarized Financial Information (Details) - CAD ($) $ in Millions		3 Months Ended			6 Months Ended
	Apr. 13, 2023	Jun. 30, 2023	Apr. 13, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Schedule of Equity Method Investments [Line Items]
Total revenues		$ 3,174		$ 2,202	$ 5,440	$ 4,040
Total operating expenses		2,230		1,334	3,667	2,637
Operating income		944		868	1,773	1,403
Income before income taxes		(6,347)		1,010	(5,384)	1,685
Net income		$ 1,324		765	$ 2,124	1,355
KCS
Schedule of Equity Method Investments [Line Items]
Total revenues	$ 164		$ 1,351	1,079		2,065
Total operating expenses	109		888	680		1,297
Operating income	55		463	399		768
Less : Other	9		83	59		98
Income before income taxes	46		380	340		670
Net income	$ 34		$ 280	$ 248		$ 485