XML 60 R43.htm IDEA: XBRL DOCUMENT
v3.21.2

Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions | 6 Months Ended |
--- | --- | ---
Jun. 30, 2021 | Dec. 31, 2020
Fair Value of Financial Instruments [Line Items] |  |
Investments not required to be disclosed | $ 338 | $ 322
NUG contracts |  |
Fair Value of Financial Instruments [Line Items] |  |
Period of future observable data to determine contract price | 2 years |

X
- Definition Derivative, Contract Price, Period of Future Observable Data + References No definition available. + Details
Name: | fe_DerivativeContractPricePeriodOfFutureObservableData
Namespace Prefix: | fe_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair Value of Financial Instruments. + References No definition available. + Details
Name: | fe_FairValueOfFinancialInstrumentsLineItems
Namespace Prefix: | fe_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Investments not required to be disclosed. + References No definition available. + Details
Name: | fe_InvestmentsNotRequiredToBeDisclosed
Namespace Prefix: | fe_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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