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Discontinued Operations - Narrative (Details) $ in Millions |  |  |  | 1 Months Ended | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Apr. 06, 2018 USD ($) | Mar. 16, 2018 USD ($) | Mar. 09, 2018 USD ($) MW | Aug. 31, 2017 Natural_gas_plant MW | Sep. 30, 2018 USD ($) | Mar. 31, 2018 USD ($) | Sep. 30, 2017 USD ($) | Dec. 31, 2018 USD ($) | Sep. 30, 2018 USD ($) | Sep. 30, 2017 USD ($) | May 11, 2018 USD ($) | Dec. 31, 2017 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Short-term borrowings |  |  |  |  | $ 1,700.0 |  |  |  | $ 1,700.0 |  |  | $ 300.0
Interest accrued |  |  |  |  | 255.0 |  | $ 262.0 |  | 858.0 | $ 751.0 |  |
Purchase Agreement with Subsidiary of LS Power |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Plant capacity (in MW's) | MW |  |  |  | 1,615 |  |  |  |  |  |  |  |
AE Supply | Purchase Agreement with Subsidiary of LS Power |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of gas generating plants | Natural_gas_plant |  |  |  | 4 |  |  |  |  |  |  |  |
AGC | Purchase Agreement with Subsidiary of LS Power |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage |  |  |  | 59.00% |  |  |  |  |  |  |  |
Pleasants Power Station | Purchase Agreement with Subsidiary of LS Power |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Plant capacity (in MW's) | MW |  |  |  | 1,300 |  |  |  |  |  |  |  |
Bay Shore Unit 1 | Asset Purchase Agreement with Walleye Energy, LLC |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Plant capacity (in MW's) | MW |  |  | 136 |  |  |  |  |  |  |  |  |
Promissory Notes | FES and FENOC |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest accrued |  |  |  |  | 8.0 |  |  |  | 16.0 |  |  |
Promissory Notes | AE Supply | FES and FENOC |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Outstanding borrowings |  |  |  |  | 102.0 |  |  |  | 102.0 |  |  |
Revolving Credit Facility | Line of Credit | FES |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Line of credit outstanding |  |  | $ 500.0 |  | 500.0 |  |  |  | 500.0 |  |  |
Loan reserves |  |  |  |  |  | $ 500.0 |  |  |  |  |  |
Money Pool | FES and FENOC |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Short-term borrowings |  | $ 4.0 |  |  |  |  |  |  |  |  |  |
Reinstated debt under settlement agreement |  | 88.0 |  |  |  |  |  |  |  |  |  |
Money Pool | Adjustment | FES and FENOC |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Short-term borrowings |  | $ 92.0 |  |  |  |  |  |  |  |  |  |
Discontinued Operations, Disposed of by Means Other than Sale | FES and FENOC |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Investments in subsidiaries |  |  |  |  | 0.0 |  |  |  | 0.0 |  |  |
Assumption of benefit obligations retained at FE (including Pension, OPEB and EDCP) |  |  |  |  | 0.0 | (820.0) |  |  | 820.0 |  |  |
Settlement payments | $ 72.0 |  |  |  |  |  |  |  |  |  |  |
Terms of settlement agreement |  |  |  |  |  |  |  |  | 66.0 |  |  |
Estimated tax payments that have been made |  |  |  |  |  |  |  |  | 20.0 |  |  |
Tax consequence of outside basis difference |  |  |  |  | 950.0 |  |  |  | 950.0 |  |  |
Other Current Liabilities | Discontinued Operations, Disposed of by Means Other than Sale | FES and FENOC |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Indemnification obligation |  |  |  |  |  |  |  |  |  |  | $ 58.0 |
Services Agreements | Affiliated Companies | Discontinued Operations, Disposed of by Means Other than Sale | FES | FES and FENOC |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Amounts of transaction |  |  |  |  |  |  |  |  | 110.0 |  |  |
Services Agreements | Affiliated Companies | Discontinued Operations, Disposed of by Means Other than Sale | Scenario, Forecast | FES | FES and FENOC |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Amounts of transaction |  |  |  |  |  |  |  | $ 112.5 |  |  |  |
Power Purchase Agreements | Affiliated Companies | Discontinued Operations, Disposed of by Means Other than Sale | FES | FES and FENOC |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Due from related parties |  |  |  |  | 21.0 |  |  |  | 21.0 |  |  |
Purchases from related party |  |  |  |  | 74.0 |  |  |  | 248.0 |  |  |
Tax Allocation Agreement | Affiliated Companies | Discontinued Operations, Disposed of by Means Other than Sale | FES and FENOC |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Due from related parties |  |  |  |  | 88.0 |  |  |  | 88.0 |  |  |
FE | Promissory Notes | FES and FENOC |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Loan reserves |  |  |  |  | $ 8.0 | 102.0 |  |  | $ 16.0 |  |  |
FE | Unregulated Money Pool [Member] | FES and FENOC |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Loan reserves |  |  |  |  |  | 92.0 |  |  |  |  |  |
FE | Money Pool | FES and FENOC |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Loan reserves |  |  |  |  |  | 4.0 |  |  |  |  |  |
FE | Reinstated Debt under Money Pool [Member] | FES and FENOC |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Loan reserves |  |  |  |  |  | $ 88.0 |  |  |  |  |  |

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