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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, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Financial Instruments [Abstract] |  |  |
Net realized risk management loss (gain) | $ 64 | $ (99) | $ (2)
Net unrealized risk management loss (gain) | 13 | (35) | 37
Gains (losses) on change in fair value of derivatives | $ 77 | $ (134) | $ 35

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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 Settled Derivatives + References No definition available. + Details
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- Definition Gain (Losses) On Change In Fair Value Of Unsettled 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 2019-01-01 -Paragraph 85 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_85&doctype=Standard -URIDate 2019-03-27 + Details
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