Business acquisition - Narrative (Details)				3 Months Ended		12 Months Ended
	Dec. 31, 2023 CAD ($)	Apr. 14, 2023 CAD ($)	Apr. 13, 2023 CAD ($) renewal_period	Mar. 31, 2024 CAD ($)	Apr. 13, 2023 CAD ($)	Dec. 31, 2024 CAD ($)	Dec. 31, 2023 CAD ($)	Dec. 31, 2022 CAD ($)	Dec. 14, 2021
Business Acquisition [Line Items]
Rail investments accounted for on an equity basis			$ 44,402,000,000		$ 44,402,000,000
Remeasurement loss of Kansas City Southern						$ 0	$ 7,175,000,000	$ 0
Deferred income tax recovery						(28,000,000)	7,885,000,000	(136,000,000)
Goodwill	$ 17,729,000,000					19,350,000,000	17,729,000,000	344,000,000
Goodwill, expected tax deductible amount						0
Equity loss of Kansas City Southern					230,000,000	0	230,000,000	1,074,000,000
KCS historical, net income (loss) attributable to controlling shareholders							280,000,000	1,287,000,000
Equity loss of Kansas City Southern
Business Acquisition [Line Items]
Equity loss of Kansas City Southern							230,000,000	1,074,000,000
Kansas City Southern
Business Acquisition [Line Items]
Percentage ownership acquired									100.00%
Fair value of previously held equity method investment	$ 37,227,000,000	$ 37,227,000,000	37,227,000,000
Remeasurement loss of Kansas City Southern							7,175,000,000
Deferred income tax recovery							7,832,000,000
Accounts receivable, net			697,000,000		697,000,000
Accounts payable acquired			1,014,000,000		1,014,000,000
Intangible assets		3,022,000,000				3,022,000,000
Net working capital		51,000,000				(110,000,000)
Goodwill		$ 17,491,000,000	$ 17,632,000,000		$ 17,632,000,000	17,632,000,000
Acquisition-related costs						112,000,000	190,000,000
KCS historical, net income (loss) attributable to controlling shareholders						(352,000,000)	297,000,000
Kansas City Southern | Concession land rights
Business Acquisition [Line Items]
Property, plant and equipment, useful life			50 years		50 years
Kansas City Southern | Litigation and Personal Injury Claims
Business Acquisition [Line Items]
Net working capital			$ 15,000,000		$ 15,000,000
Liabilities arising from contingencies			44,000,000		44,000,000
Kansas City Southern | Environmental Liabilities
Business Acquisition [Line Items]
Net working capital			160,000,000		160,000,000
Liabilities arising from contingencies			40,000,000		40,000,000
Kansas City Southern | Concession Rights
Business Acquisition [Line Items]
Intangible assets			$ 9,176,000,000		9,176,000,000
Acquired finite-lived intangible assets, weighted average useful life			74 years
Number of renewal periods | renewal_period			1
Kansas City Southern | Contracts and Customer Relationships
Business Acquisition [Line Items]
Intangible assets			$ 3,022,000,000		3,022,000,000
Kansas City Southern | Contracts and Customer Relationships | Minimum
Business Acquisition [Line Items]
Acquired finite-lived intangible assets, weighted average useful life			9 years
Kansas City Southern | Contracts and Customer Relationships | Maximum
Business Acquisition [Line Items]
Acquired finite-lived intangible assets, weighted average useful life			22 years
Kansas City Southern | Purchased services and other
Business Acquisition [Line Items]
KCS historical, net income (loss) attributable to controlling shareholders						(3,000,000)	1,000,000
Kansas City Southern | Other expense (income)
Business Acquisition [Line Items]
Acquisition-related costs							6,000,000
KCS historical, net income (loss) attributable to controlling shareholders						(3,000,000)	2,000,000
Kansas City Southern | Equity loss of Kansas City Southern
Business Acquisition [Line Items]
Acquisition-related costs					$ 11,000,000			49,000,000
KCS historical, net income (loss) attributable to controlling shareholders							48,000,000
KCS earnings (loss), after deferred tax recovery								163,000,000
Kansas City Southern | Compensation and benefits
Business Acquisition [Line Items]
Other tax expense (recovery), goodwill remeasurement						(4,000,000)
Other tax expense, goodwill remeasurement				$ 10,000,000
Other tax recovery, goodwill remeasurement				$ 14,000,000
Acquisition-related costs						18,000,000	71,000,000
Kansas City Southern | Purchased services and other
Business Acquisition [Line Items]
Acquisition-related costs						88,000,000	111,000,000	$ 74,000,000
Kansas City Southern | Cost, direct material
Business Acquisition [Line Items]
Acquisition-related costs						6,000,000	2,000,000
Kansas City Southern | Depreciation, Depletion and Amortization
Business Acquisition [Line Items]
KCS historical, net income (loss) attributable to controlling shareholders						(333,000,000)	234,000,000
Kansas City Southern | Interest Revenue (Expense), Net
Business Acquisition [Line Items]
KCS historical, net income (loss) attributable to controlling shareholders						(20,000,000)	17,000,000
Kansas City Southern | Net Income (Loss) Attributable to Noncontrolling Interest
Business Acquisition [Line Items]
KCS historical, net income (loss) attributable to controlling shareholders						$ 7,000,000	$ 5,000,000