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Acquisitions, Discontinued Operations and Dispositions - Narrative (Details) - USD ($) $ in Millions |  |  |  | 1 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | --- | ---
Jul. 16, 2018 | Apr. 27, 2018 | Mar. 22, 2018 | Dec. 31, 2017 | Jun. 30, 2018 | Dec. 31, 2017
GenOn Entities |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Pension liability |  |  |  |  | $ 90.0 |
Liability, other postretirement-employment and retiree heal and welfare benefits |  |  |  |  | 25.0 |
GenOn Entities |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Settlement consideration |  |  |  |  | 261.3 |
Professional fees |  | $ 6.0 |  |  |  |
GenOn Entities | Services Agreement |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Credit applied |  |  |  |  |  | $ 28.0
Shared services, annualized rate |  |  |  | $ 84.0 |  | 84.0
Plan of Reorganization |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Intercompany secured revolving credit facility and accrued interest and fees |  |  |  |  | $ 151.0 |
Percentage of aggregate principal amount |  |  |  |  | 93.00% |
Payment of pension contributions |  |  |  | 13.0 |  | 13.0
Plan of Reorganization | GenOn Mid-Atlantic | Intercompany Credit Agreement | Letter of Credit |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Letters of credit |  | $ 37.5 |  |  |  |
Plan of Reorganization | Services Agreement |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Credit applied |  |  |  |  |  | 28.0
Payment to affiliate |  |  |  |  | $ 18.0 |
Shared services, annualized rate |  |  |  | 84.0 |  | $ 84.0
Plan of Reorganization | Services Agreement | GenOn Entities |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Payment to affiliate |  |  | $ 13.5 | $ 15.0 |  |
Subsequent Event | GenOn Entities |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Settlement consideration | $ 261.0 |  |  |  |  |
Subsequent Event | GenOn Entities | Assignment Of Historical Claims Against REMA |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Remaining payments and other balances due | 8.0 |  |  |  |  |
Subsequent Event | GenOn Entities | Reduction Of Settlement Payment |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Remaining payments and other balances due | 4.2 |  |  |  |  |
Subsequent Event | GenOn Entities | Indemnification Of Potential Claims By REMA (up to) |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Remaining payments and other balances due | 10.0 |  |  |  |  |
Subsequent Event | Plan of Reorganization | Services Agreement | GenOn Entities |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Payment to affiliate | 15.0 |  |  |  |  |
Subsequent Event | Plan of Reorganization | GenOn Entities |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Payments to affiliate, settlement agreement | 125.0 |  |  |  |  |
Subsequent Event | Plan of Reorganization | GenOn Entities | Services Agreement |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Credit applied | 28.0 |  |  |  |  |
Remaining payments and other balances due | 10.0 |  |  |  |  |
Subsequent Event | Plan of Reorganization | GenOn Entities | Revolving Credit Facility Borrowings |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Intercompany secured revolving credit facility and accrued interest and fees | 151.0 |  |  |  |  |
Subsequent Event | Plan of Reorganization | GenOn Entities | Accrued Interest On Borrowings |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Intercompany secured revolving credit facility and accrued interest and fees | 12.0 |  |  |  |  |
Subsequent Event | Plan of Reorganization | GenOn Entities | Other |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Remaining payments and other balances due | $ 6.0 |  |  |  |  |

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