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LEASES -Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Lessor, Lease, Description [Line Items]
Maximum potential loss of lease agreement	$ 16
Amount of leases not yet commenced	$ 14
Expected commencement period	18 months
Minimum
Lessor, Lease, Description [Line Items]
Renewal term of lease yet to be commenced	1 year
Operating lease renewal term	5 years
Maximum
Lessor, Lease, Description [Line Items]
Renewal term of lease yet to be commenced	40 years
Operating lease renewal term	10 years

X

- Definition

Lessee, Operating Lease, Lease Not yet Commenced, Amount

+ References

No definition available.

+ Details

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Namespace Prefix:	fe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Lessee, Operating Lease, Lease Not yet Commenced, Expected Commencement Period

+ References

No definition available.

+ Details

Name:	fe_LesseeOperatingLeaseLeaseNotyetCommencedExpectedCommencementPeriod
Namespace Prefix:	fe_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Lessee, Operating Lease, Residual Value Guarantee, Potential Loss

+ References

No definition available.

+ Details

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Namespace Prefix:	fe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Term of lessee's operating lease renewal for lease not yet commenced, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918673-209980

+ Details

Name:	us-gaap_LesseeOperatingLeaseLeaseNotYetCommencedRenewalTerm1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Term of lessee's operating lease renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918673-209980

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
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_LessorLeaseDescriptionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

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

X

- Details

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Namespace Prefix:
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Balance Type:
Period Type: