XML 97 R80.htm IDEA: XBRL DOCUMENT
v3.20.4

FAIR VALUE MEASUREMENTS - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments not required to be disclosed | $ 322 | $ 299
NUG contracts |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [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 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
- 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_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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