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Impairment Charges and Reversals - Summary of Increase (Decrease) to Recoverable Amount (Detail) $ in Millions | 12 Months Ended
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Dec. 31, 2020 CAD ($)
Clearwater [Member] | One Percent Increase in the Discount Rate [Member] |
Disclosure of estimation uncertainty with significant risk of causing material adjustment [line items] |
Increase (decrease) to recoverable amount | $ (5)
Clearwater [Member] | One Percent Decrease in the Discount Rate [Member] |
Disclosure of estimation uncertainty with significant risk of causing material adjustment [line items] |
Increase (decrease) to recoverable amount | 6
Clearwater [Member] | Five Percent Increase in the Forward Price Estimates [Member] |
Disclosure of estimation uncertainty with significant risk of causing material adjustment [line items] |
Increase (decrease) to recoverable amount | 52
Clearwater [Member] | Five Percent Decrease in the Forward Price Estimates [Member] |
Disclosure of estimation uncertainty with significant risk of causing material adjustment [line items] |
Increase (decrease) to recoverable amount | (97)
Elmworth-Wapiti [Member] | One Percent Increase in the Discount Rate [Member] |
Disclosure of estimation uncertainty with significant risk of causing material adjustment [line items] |
Increase (decrease) to recoverable amount | (7)
Elmworth-Wapiti [Member] | One Percent Decrease in the Discount Rate [Member] |
Disclosure of estimation uncertainty with significant risk of causing material adjustment [line items] |
Increase (decrease) to recoverable amount | 8
Elmworth-Wapiti [Member] | Five Percent Increase in the Forward Price Estimates [Member] |
Disclosure of estimation uncertainty with significant risk of causing material adjustment [line items] |
Increase (decrease) to recoverable amount | 54
Elmworth-Wapiti [Member] | Five Percent Decrease in the Forward Price Estimates [Member] |
Disclosure of estimation uncertainty with significant risk of causing material adjustment [line items] |
Increase (decrease) to recoverable amount | (96)
Kaybob-Edson [Member] | One Percent Increase in the Discount Rate [Member] |
Disclosure of estimation uncertainty with significant risk of causing material adjustment [line items] |
Increase (decrease) to recoverable amount | (13)
Kaybob-Edson [Member] | One Percent Decrease in the Discount Rate [Member] |
Disclosure of estimation uncertainty with significant risk of causing material adjustment [line items] |
Increase (decrease) to recoverable amount | 14
Kaybob-Edson [Member] | Five Percent Increase in the Forward Price Estimates [Member] |
Disclosure of estimation uncertainty with significant risk of causing material adjustment [line items] |
Increase (decrease) to recoverable amount | 54
Kaybob-Edson [Member] | Five Percent Decrease in the Forward Price Estimates [Member] |
Disclosure of estimation uncertainty with significant risk of causing material adjustment [line items] |
Increase (decrease) to recoverable amount | (106)
Borger [Member] | One Percent Increase in the Discount Rate [Member] |
Disclosure of estimation uncertainty with significant risk of causing material adjustment [line items] |
Increase (decrease) to recoverable amount | (71)
Borger [Member] | One Percent Decrease in the Discount Rate [Member] |
Disclosure of estimation uncertainty with significant risk of causing material adjustment [line items] |
Increase (decrease) to recoverable amount | 81
Borger [Member] | Five Percent Increase in the Forward Price Estimates [Member] |
Disclosure of estimation uncertainty with significant risk of causing material adjustment [line items] |
Increase (decrease) to recoverable amount | 263
Borger [Member] | Five Percent Decrease in the Forward Price Estimates [Member] |
Disclosure of estimation uncertainty with significant risk of causing material adjustment [line items] |
Increase (decrease) to recoverable amount | $ (264)

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