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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 |  |  |

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