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