Amount of income (loss) for proportionate share of equity method investee's income (loss).

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Name:	us-gaap_IncomeLossFromEquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Investment in KCS - Narrative (Details) - CAD ($) $ in Millions		3 Months Ended			6 Months Ended
	Apr. 13, 2023	Jun. 30, 2024	Jun. 30, 2023	Apr. 13, 2023	Jun. 30, 2024	Jun. 30, 2023
Schedule of Equity Method Investments [Line Items]
Equity earnings of Kansas City Southern	$ 26	$ 0	$ 26	$ (230)	$ 0	$ 230
Dividend from Kansas City Southern		$ 0	$ 0		$ 0	$ 300
KCS
Schedule of Equity Method Investments [Line Items]
Dividend from Kansas City Southern	0			300
Amortization of basis difference	$ 6			$ 48