XML 128 R110.htm IDEA: XBRL DOCUMENT
v3.21.1

Derivatives Instruments (Notional Volumes of Commodity Swaps and Forward Contracts Designated for Regulatory Deferral) (Details) - Regulatory deferral - Commodity swaps and forwards - Purchases bbl in Millions, T in Millions, MWh in Millions, MMBTU in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 MMBTU MWh T bbl
Coal | 2021 |
Derivative [Line Items] |
Coal (metric tonnes) | T | 0
Coal | 2022-2023 |
Derivative [Line Items] |
Coal (metric tonnes) | T | 1
Natural gas | 2021 |
Derivative [Line Items] |
Natural Gas (Mmbtu) / Power (MWh) | MWh | MMBTU | 5
Natural gas | 2022-2023 |
Derivative [Line Items] |
Natural Gas (Mmbtu) / Power (MWh) | MWh | MMBTU | 7
Heavy fuel oil | 2021 |
Derivative [Line Items] |
Heavy fuel oil (bbls) | bbl | 0
Heavy fuel oil | 2022-2023 |
Derivative [Line Items] |
Heavy fuel oil (bbls) | bbl | 1
Power | 2021 |
Derivative [Line Items] |
Natural Gas (Mmbtu) / Power (MWh) | MWh | MWh | 2
Power | 2022-2023 |
Derivative [Line Items] |
Natural Gas (Mmbtu) / Power (MWh) | MWh | MWh | 2

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

X
- Definition Nominal volume used to calculate payments on a derivative instrument. + References No definition available. + Details
Name: | us-gaap_DerivativeNonmonetaryNotionalAmountVolume
Namespace Prefix: | us-gaap_
Data Type: | num:volumeItemType
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_DerivativeInstrumentRiskAxis=us-gaap_CommodityContractMember
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: | srt_EnergyAxis=us-gaap_PublicUtilitiesInventoryCoalMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis=ema_DerivativeInstrumentSettlementPeriodOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis=ema_DerivativeInstrumentSettlementPeriodTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_EnergyAxis=srt_FuelMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_EnergyAxis=srt_CrudeOilMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_EnergyAxis=us-gaap_ElectricityPurchasedMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |