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Derivative Instruments (Details 4) - Not Designated as Hedging Instrument - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2017 | Jun. 30, 2016 | Jun. 30, 2017 | Jun. 30, 2016
Outstanding net asset (liability) [Roll Forward] |  |  |  |
Outstanding net asset (liability), Beginning Balance | $ (105) | $ (137) | $ (105) | $ (135)
Unrealized loss | (5) |  | (11) | (12)
Purchases | 3 | 4 | 3 | 4
Settlements | 12 | 13 | 18 | 23
Outstanding net asset (liability), Ending Balance | (95) | (120) | (95) | (120)
NUGs |  |  |  |
Outstanding net asset (liability) [Roll Forward] |  |  |  |
Outstanding net asset (liability), Beginning Balance | (103) | (135) | (107) | (136)
Unrealized loss | (5) |  | (10) | (12)
Purchases | 0 | 0 | 0 | 0
Settlements | 10 | 11 | 19 | 24
Outstanding net asset (liability), Ending Balance | (98) | (124) | (98) | (124)
Regulated FTRs |  |  |  |
Outstanding net asset (liability) [Roll Forward] |  |  |  |
Outstanding net asset (liability), Beginning Balance | (2) | (2) | 2 | 1
Unrealized loss | 0 |  | (1) | 0
Purchases | 3 | 4 | 3 | 4
Settlements | 2 | 2 | (1) | (1)
Outstanding net asset (liability), Ending Balance | $ 3 | $ 4 | $ 3 | $ 4

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- Definition Derivative instruments not designated as hedging instruments purchases + References No definition available. + Details
Name: | fe_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsPurchases
Namespace Prefix: | fe_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Settled Contracts. + References No definition available. + Details
Name: | fe_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsSettledContracts
Namespace Prefix: | fe_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Derivative instruments not designated as hedging instruments unrealized gain (loss). + References No definition available. + Details
Name: | fe_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsUnrealizedGainLoss
Namespace Prefix: | fe_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Derivatives not designated as hedging instruments at fair value net. + References No definition available. + Details
Name: | fe_DerivativesNotDesignatedAsHedgingInstrumentsAtFairValueNet
Namespace Prefix: | fe_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Outstanding Net Asset (Liability) [Roll Forward] + References No definition available. + Details
Name: | fe_OutstandingNetAssetLiabilityRollForward
Namespace Prefix: | fe_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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

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

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