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Discontinued Operations - Narrative (Details) $ in Millions				1 Months Ended	3 Months Ended			9 Months Ended
Discontinued Operations - Narrative (Details) $ in Millions	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