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Risk Management Activities - Additional Information (Details) - CAD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | --- | ---
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |  |
Collateral paid (Note 15) | $ 42 | $ 105 |
Financial assets pledged as collateral for liabilities or contingent liabilities | 3 | 17 |
Derivative, contingent feature, additional collateral requirement | 51 | 120 |
Asset-backed debt instruments held | 920 |  |
Debt instruments held | 1,217 |  |
Commodity Price Risk - Proprietary Trading [Member] |  |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |  |
Value at risk | 1 | 2 | $ 5
Commodity Price Risk - Generation [Member] |  |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |  |
Value at risk | 25 | 18 | 16
Commodity Price Risk - Generation - Mark To Market Value [Member] |  |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |  |
Value at risk | 8 | 13 | $ 5
Letter of credit |  |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |  |
Collateral posted on derivative liabilities | $ 112 | $ 120 |

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- Definition The amount of current non-cash collateral assets (such as debt or equity instruments) provided to a transferee, for which the transferee has the right by contract or custom to sell or repledge the collateral. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 9 -IssueDate 2018-01-01 -Paragraph 3.2.23 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=9&date=2018-03-01&anchor=para_3.2.23_a&doctype=Standard -URIDate 2018-03-16 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2021-01-01 -Name IAS -Number 39 -IssueDate 2018-01-01 -Paragraph 37 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=39&date=2017-03-02&anchor=para_37_a&doctype=Standard&book=b_pdf -URIDate 2018-03-16 + Details
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- Definition The amount of instruments representing indebtedness held by the entity. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 55 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_55&doctype=Standard -URIDate 2018-03-16 + Details
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- Definition The amount of financial assets that the entity has pledged as collateral for liabilities or contingent liabilities, including amounts that have been reclassified in accordance with paragraph 3.2.23(a) of IFRS 9. [Refer: Contingent liabilities [member]; Financial assets] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2018-01-01 -Paragraph 14 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2018-03-01&anchor=para_14_a&doctype=Standard -URIDate 2018-03-16 + Details
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- Definition The measure of a potential loss exposure as a result of future market movements, based on a specified confidence interval and measurement horizon. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IFRS -Number 7 -IssueDate 2018-01-01 -Paragraph 41 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2018-03-01&anchor=para_41&doctype=Standard -URIDate 2018-03-16 + Details
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