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Derivatives Instruments (Realized and Unrealized Gains (Losses) with Respect to Cash Flow Hedges) (Details) - CAD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items] |  |
Total gains (losses) in Net income | $ 28 | $ (1)
Interest expense, net |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Unrealized gain on equity derivatives | 0 |
Operating, maintenance and general expense |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Unrealized gain on equity derivatives | 1 |
Total gains (losses) in Net income | $ 27 |
Interest rate swaps | Interest expense, net |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Unrealized gain on equity derivatives |  | (1)
Interest rate swaps | Operating, maintenance and general expense |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Unrealized gain on equity derivatives |  | 0
Total gains (losses) in Net income |  | $ 0

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- Definition Amount of increase (decrease) in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959 + Details
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- Definition Amount of gain (loss) included in earnings for the period from the increase (decrease) in fair value of interest rate derivatives not designated as hedging instruments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624171-113959 + Details
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