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Regulatory Assets and Liabilities (Regulated Assets) (Details) - CAD CAD in Millions | Dec. 31, 2016 | Dec. 31, 2015
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Regulatory Assets [Line Items] |  |
Regulatory Assets, Current | CAD 80 | CAD 94
Regulatory Assets, Noncurrent | 1,242 | 605
Regulatory Assets, Total | 1,322 | 699
Deferred income tax regulatory assets [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets, Total | 632 | 431
Pension and post-retirement medical plan [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets, Total | 373 | 12
Environmental remediations [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets, Total | 49 | 0
Unamortized Defeasance Costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets, Total | 39 | 46
GBPC Hurricane Matthew restoration [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets, Total | 28 | 0
Demand Side Management [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets, Total | 32 | 36
Stranded cost recovery [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets, Total | 27 | 28
Deferrals related to derivative instruments [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets, Total | 15 | 68
Debt Basis Adjustment [Member] [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets, Total | 19 | 0
Deferred Bond Refinancing Costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets, Total | 9 | 0
Cost Recovery Clauses [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets, Total | 12 | 0
Fuel Adjustment Mechanism Asset [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets, Total | 0 | 14
Fuel Adjustment Mechanism Asset [Member] | Regulated Operation [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets, Current | 0 | 14
Other Regulatory Assets (Liabilities) [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets, Total | CAD 87 | CAD 64

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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- Definition Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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