XML 119 R102.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Derivatives (Master Netting Agreements) (Details) - CAD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract] |  |
Derivative Asset, Collateral, Obligation to Return Cash, Offset | $ 181 | $ 131
Derivative Liability, Fair Value, Amount Not Offset Against Collateral [Abstract] |  |
Derivative Liability, Collateral, Right to Reclaim Cash, Offset | 181 | 131
Designated as Hedging Instrument [Member] | Regulatory Deferral Hedge [Member] |  |
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract] |  |
Derivative Asset, Collateral, Obligation to Return Cash, Offset | 14 | 10
Derivative Liability, Fair Value, Amount Not Offset Against Collateral [Abstract] |  |
Derivative Liability, Collateral, Right to Reclaim Cash, Offset | 14 | 10
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] |  |
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract] |  |
Derivative Asset, Collateral, Obligation to Return Cash, Offset | 167 | 121
Derivative Liability, Fair Value, Amount Not Offset Against Collateral [Abstract] |  |
Derivative Liability, Collateral, Right to Reclaim Cash, Offset | $ 167 | $ 121

X
- Definition Amount of obligation to return cash collateral under master netting arrangements 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 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 + Details
Name: | us-gaap_DerivativeAssetCollateralObligationToReturnCashOffset
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_DerivativeAssetFairValueNetAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of right to receive cash collateral under master netting arrangements offset against derivative liabilities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 + Details
Name: | us-gaap_DerivativeLiabilityCollateralRightToReclaimCashOffset
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_DerivativeLiabilityFairValueNetAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=ema_RegulatoryDeferralHedgeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=ema_HeldForTradingHedgeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |