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Revenue (Remaining Performance Obligations) (Narrative) (Details) - CAD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
6. Revenue |  |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Explanation | 2040 | 2040
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items] |  |
Revenue, Remaining Performance Obligation, Amount | $ 464 | $ 347
SeaCoast Gas Transmission, LLC | PGS |  |
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items] |  |
Revenue, Remaining Performance Obligation, Amount | $ 149 |

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- Definition Description of when remaining performance obligation is expected to be recognized as revenue. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 13 -Subparagraph (b)(2) -URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130556-203045 + Details
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