Regulatory Assets and Liabilities (Regulated Assets) (Details) - CAD CAD in Millions	Dec. 31, 2016	Dec. 31, 2015
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

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.

No definition available.

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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

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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

+ References

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