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INVENTORY - Narrative (Details) - CAD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Inventories [Abstract] |  |
Write-down of product inventory | $ 33 | $ 73

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- Definition Inventories [Abstract] + References No definition available. + Details
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Namespace Prefix: | cnq_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The amount recognised resulting from the write-down of inventories to net realisable value or reversals of those write-downs. [Refer: Inventories] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 98 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_98_a&doctype=Standard -URIDate 2017-03-09 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration