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Derivatives (Credit Risk Exposure) (Details) - CAD CAD in Millions | 12 Months Ended
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Dec. 31, 2016 | Dec. 31, 2015
Credit Derivatives [Line Items] |  |
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure | CAD 1,290 | CAD 996
Total cash deposits/collateral on hand | 107 | 91
Accounts Receivable [Member] |  |
Credit Derivatives [Line Items] |  |
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure | 1,019 | 901
Total cash deposits/collateral on hand | 271 | 94
Financial assets, considered to be past due | CAD 104 | 83
Derivative, Credit Risk, Past Due Days Outstanding | 69 days |
Fair Value of assets | CAD 91 | CAD 72

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- Definition The average days outstanding on financial assets related to derivatives expressed as PnYnMnDTnHnMnS. + References No definition available. + Details
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- Definition Amount of finacial assets that are past due related to Derivatives. + References No definition available. + Details
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- Definition Net amount after allowance for doubtful accounts of finacial assets that are past due related to Derivatives. + References No definition available. + Details
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Namespace Prefix: | ema_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Maximum amount of loss due to credit risk that, based on the gross fair value of the financial instrument, the entity would incur if parties to the financial instruments that make up the concentration failed completely to perform according to the terms of the contracts and the collateral or other security, if any, for the amount due proved to be of no value to the entity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 21 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13537-108611 + Details
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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 Amount of obligation to return cash collateral under master netting arrangements that have not been offset against derivative assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 8 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=64837297&loc=d3e41678-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226016-175313 + Details
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- Details
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