Income Taxes - Narrative (Details) $ in Millions, $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2022 CAD ($)	Sep. 30, 2021 CAD ($)	Sep. 30, 2022 CAD ($)	Sep. 30, 2021 CAD ($)	Sep. 30, 2021 USD ($)
Business Acquisition [Line Items]
Deferred income tax recovery from rate decrease	$ 12		$ 12
Effective tax rate	18.01%	26.36%	18.97%	21.00%	21.00%
Effective tax rate, excluding discrete items	24.25%	24.60%	24.25%	24.60%	24.60%
Acquisition-related costs	$ 0	$ 83	$ 0	$ 295
Effective Income Tax Rate Reconciliation, Basis Difference On Equity Method Investment	(9)		8
Foreign exchange loss (gain) on debt and lease liabilities	0	46	0	(39)
Merger termination fee	0	0	0	845	$ 700
KCS
Business Acquisition [Line Items]
Acquisition-related costs	18	98	57	442
Merger termination fee				845	$ 700
KCS \| Purchased services and other
Business Acquisition [Line Items]
Acquisition-related costs	$ 18	$ 15	$ 57	$ 147

Effective Income Tax Rate Reconciliation, Basis Difference On Equity Method Investment

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Effective Income Tax Rate Reconciliation, Estimated Rate, Excluding Discrete Items, Percent

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The aggregate foreign currency transaction gain or loss on long-term debt (both realized and unrealized) and lease liabilities included in determining net income for the reporting period net of hedging activity.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Gain (loss) related to the termination of a contract between the parties. The termination may be due to many causes including early termination of a lease by a lessee, a breach of contract by one party, or a failure to perform.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to tax exempt income, equity in earnings (loss) of an unconsolidated subsidiary, minority noncontrolling interest income (loss), tax holiday, disposition of a business, disposition of an asset, repatriation of foreign earnings, repatriation of foreign earnings jobs creation act of 2004, increase (decrease) in enacted tax rate, prior year income taxes, increase (decrease) in deferred tax asset valuation allowance, and other adjustments.

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