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Asset Impairment Charges and Reversals (Details) - CAD ($) $ in Millions |  |  | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Jun. 28, 2018 | Jan. 26, 2017 | Sep. 30, 2018 | Jun. 30, 2017 | Sep. 30, 2018 | Dec. 31, 2018 | Dec. 31, 2016 | May 31, 2018
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |  |  |
Write-downs (reversals of write-downs) of property, plant and equipment |  |  |  |  |  | $ 23 |  |
Sundance Unit 2 |  |  |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |  |  |
Impairment loss |  |  |  |  | $ 38 |  |  |
Lakeswind |  |  |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |  |  |
Impairment loss | $ 12 |  |  |  |  |  |  |
Discount rate |  |  |  |  |  |  |  | 7.00%
Sundance Unit 1 |  |  |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |  |  |
Impairment loss |  |  | $ 38 | $ 20 |  |  |  |
Wintering Hills |  |  |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |  |  |
Equity participation percentage |  | 51.00% |  |  |  |  |  |
Cash transferred |  | $ 61 |  |  |  |  |  |
Wintering Hills | Wind and Solar |  |  |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |  |  |
Decrease through classified as held for sale, investment property |  |  |  |  |  |  | $ 28 |
Property, plant, and equipment | Lakeswind |  |  |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |  |  |
Impairment loss | 11 |  |  |  |  |  |  |
Intangible assets | Lakeswind |  |  |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |  |  |
Impairment loss | $ 1 |  |  |  |  |  |  |

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- Definition The decrease in investment property through classification as held for sale or inclusion in a disposal group classified as held for sale. [Refer: Disposal groups classified as held for sale [member]; Property, plant and equipment; Investment property; Disposal groups classified as held for sale [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 40 -IssueDate 2017-01-01 -Paragraph 76 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=40&date=2017-03-01&anchor=para_76_c&doctype=Standard -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 40 -IssueDate 2017-01-01 -Paragraph 79 -Subparagraph d -Clause iii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=40&date=2017-03-01&anchor=para_79_d_iii&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The amount recognised as a reduction of the carrying amount of an asset or cash-generating unit to its recoverable amount. [Refer: Carrying amount [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 36 -IssueDate 2017-01-01 -Paragraph 130 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2017-03-01&anchor=para_130_b&doctype=Standard -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 36 -IssueDate 2017-01-01 -Paragraph 130 -Subparagraph d -Clause ii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2017-03-01&anchor=para_130_d_ii&doctype=Standard -URIDate 2017-03-09 + Details
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