Gain on sale of equity investment (Details) $ in Millions, $ in Millions		3 Months Ended		9 Months Ended
	Apr. 01, 2025 USD ($)	Sep. 30, 2025 CAD ($)	Sep. 30, 2024 CAD ($)	Sep. 30, 2025 CAD ($)	Sep. 30, 2025 USD ($)	Sep. 30, 2024 CAD ($)
Schedule of Equity Method Investments [Line Items]
Proceeds from sale of equity method investments		$ 0	$ 0	$ 493		$ 0
Gain on sale of equity investment		$ 0	$ 0	333		$ 0
Panama Canal Railway Company
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage sold	50.00%
Equity method investments, Gross sale amount	$ 350
Proceeds from sale of equity method investments				493	$ 344
Gain on sale of equity investment				333	232
Equity method investment, realized gain on disposal, after tax				$ 282	$ 196