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Interest Expense, Net (Details) - CAD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016
Debt Instrument [Line Items] |  |
Interest on debt | $ 663 | $ 443
Beneficial Conversion Feature, net of tax | 0 | (43)
Beneficial Conversion Feature, before tax | 0 | 62
Allowance for Funds Used During Construction | (7) | (13)
Other | 42 | 17
Interest Expense (Income), Net | 698 | 585
Revolving Credit Facility [Member] |  |
Debt Instrument [Line Items] |  |
Interest on debt | 0 | 11
Convertible Debt [Member] |  |
Debt Instrument [Line Items] |  |
Interest on debt | $ 0 | $ 65

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- Definition Amount of a favorable spread to a debt holder between the amount of debt being converted and the value of the securities received upon conversion. This is an embedded conversion feature of convertible debt issued that is in-the-money at the commitment date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21538-112644 + Details
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- Definition Amount capitalized of allowance for funds used during construction. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430 + Details
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