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FINANCIAL INSTRUMENTS - Net (gains) losses from risk management activities (Details) - CAD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Financial Instruments [Abstract] |  |  |
Net realized risk management (gain) loss | $ (2) | $ 8 | $ (843)
Net unrealized risk management loss | 37 | 25 | 374
Gains (losses) on change in fair value of derivatives | $ (35) | (33) | 469
Gains (losses) on change in fair value of derivatives |  | $ (33) | $ 469

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- Definition Financial Instruments [Abstract] + References No definition available. + Details
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- Definition Gain (Losses) On Change In Fair Value Of Derivatives Not Designated As Hedging Instruments And Gain (Loss) On Hedge Ineffectiveness + References No definition available. + Details
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- Definition Gain (Losses) On Change In Fair Value Of Settled Derivatives + References No definition available. + Details
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- Definition The gains (losses) resulting from change in the fair value of derivatives recognised in profit or loss. [Refer: Derivatives [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 85 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_85&doctype=Standard -URIDate 2017-03-09 + Details
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