XML 125 R108.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Derivatives (Notional Volumes of Outstanding HFT Derivatives) (Details) MWh in Millions, MMBTU in Millions, $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 USD ($) MMBTU MWh
Foreign Exchange Option [Member] | 2018 [Member} |
Derivative [Line Items] |
Derivative, Notional Amount | $ | $ 2
Foreign Exchange Option [Member] | 2019 [Member] |
Derivative [Line Items] |
Derivative, Notional Amount | $ | 4
Foreign Exchange Option [Member] | 2020 [Member] |
Derivative [Line Items] |
Derivative, Notional Amount | $ | 0
Foreign Exchange Option [Member] | 2021 [Member] |
Derivative [Line Items] |
Derivative, Notional Amount | $ | 0
Foreign Exchange Option [Member] | 2022 [Member] |
Derivative [Line Items] |
Derivative, Notional Amount | $ | $ 0
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Natural Gas [Member] | Sales [Member] | 2018 [Member} |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 250
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Natural Gas [Member] | Sales [Member] | 2019 [Member] |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 56
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Natural Gas [Member] | Sales [Member] | 2020 [Member] |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 21
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Natural Gas [Member] | Sales [Member] | 2021 [Member] |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 8
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Natural Gas [Member] | Sales [Member] | 2022 [Member] |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 2
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Natural Gas [Member] | Cost of Sales [Member] | 2018 [Member} |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 325
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Natural Gas [Member] | Cost of Sales [Member] | 2019 [Member] |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 134
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Natural Gas [Member] | Cost of Sales [Member] | 2020 [Member] |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 62
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Natural Gas [Member] | Cost of Sales [Member] | 2021 [Member] |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 44
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Natural Gas [Member] | Cost of Sales [Member] | 2022 [Member] |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 41
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Power [Member] | Sales [Member] | 2018 [Member} |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 8
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Power [Member] | Sales [Member] | 2019 [Member] |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 1
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Power [Member] | Sales [Member] | 2020 [Member] |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 0
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Power [Member] | Sales [Member] | 2021 [Member] |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 0
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Power [Member] | Sales [Member] | 2022 [Member] |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 0
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Power [Member] | Cost of Sales [Member] | 2018 [Member} |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 7
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Power [Member] | Cost of Sales [Member] | 2019 [Member] |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 2
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Power [Member] | Cost of Sales [Member] | 2020 [Member] |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 0
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Power [Member] | Cost of Sales [Member] | 2021 [Member] |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 0
Designated as Hedging Instrument [Member] | Held for Trading Hedge [Member] | Power [Member] | Cost of Sales [Member] | 2022 [Member] |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 0

X
- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
Name: | invest_DerivativeNotionalAmount
Namespace Prefix: | invest_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

X
- 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
Name: | us-gaap_DerivativeLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Nominal energy measure used to calculate payments on a derivative instrument. + References No definition available. + Details
Name: | us-gaap_DerivativeNonmonetaryNotionalAmountEnergyMeasure
Namespace Prefix: | us-gaap_
Data Type: | num:energyItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeOptionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ema_FutureMaturitiesOfDerivativeNotionalAmountsInYearsAxis=ema_YearOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ema_FutureMaturitiesOfDerivativeNotionalAmountsInYearsAxis=ema_YearTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ema_FutureMaturitiesOfDerivativeNotionalAmountsInYearsAxis=ema_YearThreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ema_FutureMaturitiesOfDerivativeNotionalAmountsInYearsAxis=ema_YearFourMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ema_FutureMaturitiesOfDerivativeNotionalAmountsInYearsAxis=ema_YearFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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_HeldForTradingHedgeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EnergyAxis=ema_NaturalGasMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=us-gaap_SalesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=us-gaap_CostOfSalesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EnergyAxis=ema_PowerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |