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Income Taxes - Significant Components of Deferred Income Tax Assets (Liabilities) (Details) - CAD ($) $ in Millions | Dec. 31, 2024 | Dec. 31, 2023
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Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Unrecognized deferred income tax assets | $ (52) | $ (21)
Net deferred tax liabilities | (418) | (365)
Cost | Non-capital losses |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Net deferred income tax liabilities, before unrecognized deferred income tax assets | 149 | 88
Cost | Future decommissioning and restoration costs |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Net deferred income tax liabilities, before unrecognized deferred income tax assets | 184 | 140
Cost | Property, plant and equipment |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Net deferred income tax liabilities, before unrecognized deferred income tax assets | (646) | (528)
Cost | Investment in subsidiaries |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Net deferred income tax liabilities, before unrecognized deferred income tax assets | (60) | (63)
Cost | Risk management assets and liabilities, net |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Net deferred income tax liabilities, before unrecognized deferred income tax assets | 40 | 99
Cost | Employee future benefits and compensation plans |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Net deferred income tax liabilities, before unrecognized deferred income tax assets | 52 | 50
Cost | Foreign exchange differences |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Net deferred income tax liabilities, before unrecognized deferred income tax assets | 16 | 12
Cost | Other taxable temporary differences |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Net deferred income tax liabilities, before unrecognized deferred income tax assets | (1) | (6)
Accumulated impairment |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Net deferred income tax liabilities, before unrecognized deferred income tax assets | (266) | (208)
Unrecognized deferred income tax assets | $ (152) | $ (157)

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- Definition The amounts of income taxes recoverable in future periods in respect of: (a) deductible temporary differences; (b) the carryforward of unused tax losses; and (c) the carryforward of unused tax credits. [Refer: Temporary differences [member]; Unused tax credits [member]; Unused tax losses [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2024-01-01 -Paragraph 81 -Subparagraph g -Clause i -URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=12&code=ifrs-tx-2024-en-r&anchor=para_81_g_i&doctype=Standard -URIDate 2024-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2024-01-01 -Paragraph 54 -Subparagraph o -URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2024-en-r&anchor=para_54_o&doctype=Standard -URIDate 2024-03-27 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2024-01-01 -Paragraph 56 -URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2024-en-r&anchor=para_56&doctype=Standard -URIDate 2024-03-27 + Details
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- Definition The amount of deferred tax liabilities or assets. [Refer: Deferred tax liabilities; Deferred tax assets] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2024-01-01 -Paragraph 81 -Subparagraph g -Clause i -URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=12&code=ifrs-tx-2024-en-r&anchor=para_81_g_i&doctype=Standard -URIDate 2024-03-27 + Details
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