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Net Earnings Per Common Share - Narrative (Details) - shares shares in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Earnings per share [abstract] |  |  |
Potentially anti-dilutive securities (in shares) | 36,834 | 23,458 | 17,547

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- Definition Antidilutive Securities Excluded From Computation Of Earnings Per Share, Amount1 + References No definition available. + Details
Name: | cnq_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount1
Namespace Prefix: | cnq_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | ifrs-full_EarningsPerShareAbstract
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration