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Income Taxes - Significant Components of Deferred Income Tax Assets (Liabilities) (Details) - CAD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020
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Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Unrecognized deferred income tax assets | $ (64) | $ (51)
Net deferred tax liabilities | (290) | (345)
Gross carrying amount | Net operating loss carryforwards |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Deferred tax liability (asset) | 530 | 469
Gross carrying amount | Future decommissioning and restoration costs |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Deferred tax liability (asset) | 183 | 140
Gross carrying amount | Property, plant and equipment |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Deferred tax liability (asset) | (651) | (717)
Gross carrying amount | Risk management assets and liabilities, net |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Deferred tax liability (asset) | (53) | (107)
Gross carrying amount | Employee future benefits and compensation plans |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Deferred tax liability (asset) | 53 | 62
Gross carrying amount | Interest deductible in future periods |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Deferred tax liability (asset) | 17 | 22
Gross carrying amount | Foreign exchange differences on US-denominated debt |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Deferred tax liability (asset) | 16 | 31
Gross carrying amount | Other deductible temporary differences |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Deferred tax liability (asset) | (5) | 2
Accumulated impairment |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Deferred tax liability (asset) | 90 | (98)
Unrecognized deferred income tax assets | $ (380) | $ (247)

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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 2021-01-01 -Paragraph 81 -Subparagraph g -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2021-en-r&anchor=para_81_g_i&doctype=Standard -URIDate 2021-03-24 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2021-01-01 -Paragraph 54 -Subparagraph o -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2021-en-r&anchor=para_54_o&doctype=Standard -URIDate 2021-03-24 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2021-01-01 -Paragraph 56 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2021-en-r&anchor=para_56&doctype=Standard -URIDate 2021-03-24 + 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 2021-01-01 -Paragraph 81 -Subparagraph g -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2021-en-r&anchor=para_81_g_i&doctype=Standard -URIDate 2021-03-24 + Details
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- Definition The amount of deferred tax liabilities net of deferred tax assets, when the absolute amount of deferred tax liabilities is greater than the absolute amount of deferred tax assets. [Refer: Deferred tax assets; Deferred tax liabilities] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 12 -IssueDate 2021-01-01 -Paragraph 81 -Subparagraph g -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2021-en-r&anchor=para_81_g_i&doctype=Standard -URIDate 2021-03-24 + Details
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