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Organization and Basis of Presentation (Details Textuals) customer in Millions, $ in Millions | 3 Months Ended | 9 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Sep. 30, 2018 USD ($) transmission_center company MW | Mar. 31, 2018 USD ($) | Sep. 30, 2017 USD ($) | Dec. 31, 2018 USD ($) | Sep. 30, 2018 USD ($) customer transmission_center company mi MW | Sep. 30, 2017 USD ($) | Sep. 26, 2018 USD ($) | Jan. 01, 2018 USD ($) | Aug. 31, 2017 MW
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Length of transmission lines | mi |  |  |  |  | 24,500 |  |  |  |
Number of regional transmission centers | transmission_center | 2 |  |  |  | 2 |  |  |  |
Cash payment |  |  |  |  |  |  | $ 225.0 |  |
Capitalized cost of equity | $ 11.0 |  | $ 8.0 |  | $ 33.0 | $ 25.0 |  |  |
Capitalized interest | $ 5.0 |  | 5.0 |  | $ 14.0 | 14.0 |  |  |
Accounting Standards Update 2018-02 | Retained Earnings |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Cumulative effect of new accounting principle |  |  |  |  |  |  |  | $ 22.0 |
Regulated Distribution |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Number of existing utility operating companies | company | 10 |  |  |  | 10 |  |  |  |
Number of customers served by utility operating companies | customer |  |  |  |  | 6 |  |  |  |
Plant capacity (in MW's) | MW | 3,790 |  |  |  | 3,790 |  |  |  |
FES | Accounting Standards Update 2016-01 | Retained Earnings |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Cumulative effect of new accounting principle |  |  |  |  |  |  |  | 115.0 |
FES and FENOC | Accounting Standards Update 2018-02 | Retained Earnings |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Cumulative effect of new accounting principle |  |  |  |  |  |  |  | $ 8.0 |
Purchase Agreement with Subsidiary of LS Power |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Plant capacity (in MW's) | MW |  |  |  |  |  |  |  |  | 1,615
Discontinued Operations, Disposed of by Means Other than Sale | FES and FENOC |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Fair value of investments | $ 0.0 | $ 0.0 |  |  | $ 0.0 |  |  |  |
Gain (Loss) on disposal of FES and FENOC, net of tax | (834.0) | $ 1,200.0 | $ 0.0 |  | 405.0 | $ 0.0 |  |  |
Terms of settlement agreement |  |  |  |  | 66.0 |  |  |  |
Estimated tax payments that have been made |  |  |  |  | 20.0 |  |  |  |
Probable loss with respect to bankruptcy | (1,200.0) |  |  |  |  |  |  |  |
Discontinued Operations, Disposed of by Means Other than Sale | FES and FENOC | Tax Year 2017 |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Overpayment of NOL's waived |  |  |  |  |  |  | 71.0 |  |
Discontinued Operations, Disposed of by Means Other than Sale | FES and FENOC | Tax Year 2018 |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Overpayment of NOL's waived |  |  |  |  |  |  | 88.0 |  |
Other Operating Expense | Accounting Standards Update 2017-07 |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Effect of change on net income | (7.0) |  |  |  | (23.0) |  |  |  |
Miscellaneous Income | Accounting Standards Update 2017-07 |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Effect of change on net income | $ 7.0 |  |  |  | $ 23.0 |  |  |  |
Corporate/Other |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Plant capacity (in MW's) | MW | 1,367 |  |  |  | 1,367 |  |  |  |
Loans Payable | Intercompany Income Tax Allocation Agreement | FES |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Face amount of debt |  |  |  |  |  |  | 628.0 |  |
Line of Credit | Secured Credit Facility | FES |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Maximum amount borrowed under revolving credit facility |  |  |  |  |  |  | 500.0 |  |
Line of Credit | Credit Agreement | FES |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Maximum amount borrowed under revolving credit facility |  |  |  |  |  |  | $ 200.0 |  |
Pleasants Power Station | Purchase Agreement with Subsidiary of LS Power |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Plant capacity (in MW's) | MW |  |  |  |  |  |  |  |  | 1,300
Pleasants Power Station | McElroy's Run Impoundment Site |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Increase in asset retirement obligation | $ 43.0 |  |  |  |  |  |  |  |
Pleasants Power Station | McElroy's Run Impoundment Site | Regulation of Waste Disposal | AE Supply |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Increase in asset retirement obligation | $ 43.0 |  |  |  |  |  |  |  |
Affiliated Companies | Services Agreements | Discontinued Operations, Disposed of by Means Other than Sale | FES and FENOC | FES |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Amounts of transaction |  |  |  |  | $ 110.0 |  |  |  |
Affiliated Companies | Scenario, Forecast | Services Agreements | Discontinued Operations, Disposed of by Means Other than Sale | FES and FENOC | FES |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |
Amounts of transaction |  |  |  | $ 112.5 |  |  |  |  |

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