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Commitments, Guarantees and Contingencies - Narrative (Details) T in Millions		9 Months Ended	12 Months Ended
	Oct. 06, 2020 USD ($)	Sep. 30, 2020 USD ($) phase T	Dec. 31, 2019 USD ($)	Oct. 29, 2020 director	Nov. 12, 2019	Nov. 04, 2019 USD ($)
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated		$ 1,700,000,000
Company posted collateral related to net liability positions		$ 1,000,000
Amount of code of conduct payment			$ 4,000,000
Reduction in CO2 emissions		62.00%
Proposed goal to reduce CO2 pollution (percent)		90.00%
Noncurrent liabilities - held for sale (Note 10)		$ 718,000,000	691,000,000
Subsequent Event
Guarantor Obligations [Line Items]
Number of additional executives terminated \| director				2
Minimum \| Pending Litigation \| Mitchell v. FirstEnergy Corp. \| Subsequent Event
Guarantor Obligations [Line Items]
Loss contingency, damages sought	$ 875,000
Clean Water Act
Guarantor Obligations [Line Items]
Waste water discharge permit renewal cycle		5 years
Regulation of Waste Disposal
Guarantor Obligations [Line Items]
Accrual for environmental loss contingencies		$ 104,000,000
Environmental liabilities former gas facilities		$ 68,000,000
National Ambient Air Quality Standards
Guarantor Obligations [Line Items]
Capping of SO2 Emissions Under CSAPR \| T		2.4
Capping of NOx emissions under CSAPR \| T		1.2
National Ambient Air Quality Standards \| CSAPR
Guarantor Obligations [Line Items]
Number of phases under the EPA’s CAIR for reductions of Sulfur Dioxide and Mono-Nitrogen Oxides \| phase		2
Global Holding \| Senior Secured Term Loan \| Senior Loans \| Signal Peak, Global Rail and Affiliates
Guarantor Obligations [Line Items]
Investment ownership percentage		69.99%
FEV \| Senior Secured Term Loan \| Senior Loans \| Signal Peak \| Global Holding
Guarantor Obligations [Line Items]
Investment ownership percentage		33.33%
WMB Marketing Ventures, LLC \| Senior Secured Term Loan \| Senior Loans \| Signal Peak \| Global Holding
Guarantor Obligations [Line Items]
Investment ownership percentage		33.33333%
JCP&L, ME and PN \| Nuclear Plant Matters \| Financial Guarantee
Guarantor Obligations [Line Items]
Nuclear plant decommissioning trusts			900,000,000
Ownership interest					25.00%
FE
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated		$ 1,000,000,000.0
Other Guarantee
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated		114,000,000
Other Assurances
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated		502,000,000
Term Loan Facility due November 2024 \| Line of Credit \| Global Holding
Guarantor Obligations [Line Items]
Face amount of debt		120,000,000
EPA \| Clean Water Act
Guarantor Obligations [Line Items]
Proposed penalty amount						$ 900,000
Regulated Distribution \| TMI-2 \| Held-for-sale
Guarantor Obligations [Line Items]
Investments - held for sale		$ 881,000,000	$ 882,000,000