Investment in KCS - Summarized Financial Information (Details) $ in Millions		3 Months Ended			6 Months Ended
	Apr. 13, 2023 CAD ($)	Jun. 30, 2024 CAD ($)	Jun. 30, 2023 CAD ($)	Apr. 13, 2023 CAD ($)	Jun. 30, 2024 CAD ($)	Jun. 30, 2023 CAD ($)
Schedule of Equity Method Investments [Line Items]
Total revenues		$ 3,603	$ 3,174		$ 7,123	$ 5,440
Total operating expenses		2,336	2,230		4,707	3,667
Operating income		1,267	944		2,416	1,773
Income before income taxes		1,195	(6,347)		2,228	(5,384)
Net income		$ 905	$ 1,324		$ 1,680	$ 2,124
Daily exchange rate used, revenue	1.35			1.35
KCS
Schedule of Equity Method Investments [Line Items]
Total revenues	$ 164			$ 1,351
Total operating expenses	109			888
Operating income	55			463
Less : other	9			83
Income before income taxes	46			380
Net income	$ 34			$ 280