Investment in KCS - Summarized Financial Information (Details) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2023 CAD ($)	Apr. 13, 2023 CAD ($)	Sep. 30, 2022 CAD ($)	Sep. 30, 2023 CAD ($)	Sep. 30, 2022 CAD ($)
Schedule of Equity Method Investments [Line Items]
Total revenues	$ 3,339		$ 2,312	$ 8,779	$ 6,352
Total operating expenses	2,166		1,375	5,833	4,012
Operating income	1,173		937	2,946	2,340
Income before income taxes	1,038		1,087	(4,346)	2,772
Net income	$ 780		891	$ 2,904	$ 2,246
Canada, Dollars
Schedule of Equity Method Investments [Line Items]
Daily exchange rate used, net income		1.35			1.28
KCS
Schedule of Equity Method Investments [Line Items]
Total revenues		$ 1,351	1,152		$ 3,216
Total operating expenses		888	728		2,024
Operating income		463	424		1,192
Less : Other		83	67		164
Income before income taxes		380	357		1,028
Net income		$ 280	$ 263		$ 748