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Regulatory Assets and Liabilities (ROE of People Gas System Division) (Details) CAD in Millions, $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2016 USD ($) | Dec. 31, 2016 CAD | Dec. 31, 2016 USD ($) | Dec. 31, 2015 CAD
Public Utilities, General Disclosures [Line Items] |  |  |  |
Regulatory Assets | CAD |  | CAD 1,322 |  | CAD 699
Regulatory Assets, Current | CAD |  | 80 |  | 94
Environmental remediations [Member] |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Regulatory Assets | CAD |  | CAD 49 |  | CAD 0
Peoples Gas System Division [Member] |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Public Utilities, Approved Return on Equity, Percentage | 10.75% |  |  |
Peoples Gas System Division [Member] | Environmental remediations [Member] |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Reduction in annual depreciation | $ 16 |  |  |
Regulatory Assets |  |  | $ 32 |
Regulatory Assets, Current |  |  | $ 21 |
Depreciation | $ 16 |  |  |
Peoples Gas System Division [Member] | Maximum [Member] |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Public Utilities, Approved Return on Equity, Percentage | 11.75% |  |  |
Public Utilities, Approved Equity Capital Structure, Percentage | 11.75% |  |  |
Peoples Gas System Division [Member] | Minimum [Member] |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Public Utilities, Approved Return on Equity, Percentage | 9.75% |  |  |
Public Utilities, Approved Equity Capital Structure, Percentage | 9.25% |  |  |
Peoples Gas System Division [Member] | Mid Point [Member] |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Public Utilities, Approved Equity Capital Structure, Percentage | 10.75% |  |  |

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- Definition The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 + 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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