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Discontinued Operations - Narrative (Details) $ in Millions |  |  |  |  |  | 1 Months Ended | 3 Months Ended | 6 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
May 03, 2018 USD ($) | Apr. 06, 2018 USD ($) | Mar. 09, 2018 USD ($) MW | Mar. 01, 2018 USD ($) | Dec. 13, 2017 USD ($) | Aug. 31, 2017 Natural_gas_plant MW | Jun. 30, 2018 USD ($) | Mar. 31, 2018 USD ($) | Jun. 30, 2018 USD ($) | Jun. 30, 2017 USD ($) | May 11, 2018 USD ($) | Mar. 16, 2018 USD ($) | Dec. 31, 2017 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term borrowings |  |  |  |  |  |  | $ 1,664.0 |  | $ 1,664.0 |  |  |  | $ 300.0
Make-whole premiums |  |  |  |  |  |  |  |  | 89.0 | $ 0.0 |  |  |
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 |  |  |  |  |  |  |
Long-term debt and other long-term obligations |  |  |  |  |  |  | 305.0 |  | 305.0 |  |  |  |
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% |  |  |  |  | 59.00% |  |  |  |  |  |  |
Natural Gas Generating Plants | Purchase Agreement with Subsidiary of LS Power |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Cash purchase price | $ 355.0 |  |  |  | $ 388.0 |  |  |  |  |  |  |  |
Bath County Hydroelectric Power Station and Buchanan Generating Facility | Purchase Agreement with Subsidiary of LS Power |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Cash purchase price |  |  |  | $ 20.0 |  |  |  |  |  |  |  |  |
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] |  |  |  |  |  |  |  |  |  |  |  |  |
Outstanding borrowings |  |  |  |  |  |  | 102.0 |  | 102.0 |  |  |  |
Interest accrued |  |  |  |  |  |  | 8.0 |  | 8.0 |  |  |  |
PCRB | AE Supply | Purchase Agreement with Subsidiary of LS Power |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt | 142.0 |  |  |  |  |  |  |  |  |  |  |  |
PCRB | AE Supply and MP | Purchase Agreement with Subsidiary of LS Power |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt | 73.5 |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes | AGC | Purchase Agreement with Subsidiary of LS Power |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt and other long-term obligations | 100.0 |  |  |  |  |  |  |  |  |  |  |  |
Make-whole premiums | $ 89.0 |  |  |  |  |  |  |  |  |  |  |  |
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 |
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) |  |  |  |  |  |  |  | 820.0 |  |  |  |  |
Settlement payments |  | $ 72.0 |  |  |  |  |  |  |  |  |  |  |
Tax consequence of outside basis difference |  |  |  |  |  |  | 600.0 |  | $ 600.0 |  |  |  |
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] |  |  |  |  |  |  |  |  |  |  |  |  |
Transaction settlement period |  |  |  |  |  |  |  |  | 30 days |  |  |  |
Amounts of transaction |  |  |  |  |  |  | 41.0 |  |  |  |  |  |
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 |  |  |  |  |  |  | 23.0 |  | $ 23.0 |  |  |  |
Purchases from related party |  |  |  |  |  |  | 71.0 |  | 174.0 |  |  |  |
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 |  |  |  |  |  |  | 58.0 |  | $ 58.0 |  |  |  |
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 |  |  |  |  |
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 |  |  |  |  |

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