Discontinued Operations - Narrative (Details) $ in Millions						1 Months Ended	3 Months Ended			9 Months Ended	12 Months Ended
	May 03, 2018 USD ($)	Apr. 06, 2018 USD ($)	Mar. 16, 2018 USD ($)	Mar. 09, 2018 USD ($) MW	Feb. 18, 2018 USD ($)	Aug. 31, 2017 Natural_gas_plant MW	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) MW	Dec. 31, 2018 USD ($) MW	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	May 11, 2018 USD ($)	Mar. 06, 2017 MW
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Short-term borrowings									$ 300.0	$ 1,250.0	$ 1,250.0	$ 300.0
Interest expense											$ 1,116.0	1,005.0	$ 973.0
Purchase Agreement with Subsidiary of LS Power
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Plant generation capacity (in MW's) | MW						1,615
AE Supply
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Amount of damages awarded to other party					$ 93.0
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
Make-whole premiums	$ 89.0
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%
Pleasants Power Station
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Plant generation capacity (in MW's) | MW															1,300
Pleasants Power Station | AE Supply | Purchase Agreement with Subsidiary of LS Power
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Plant generation capacity (in MW's) | MW										1,300	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 expense											$ 24.0
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
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]
Long-term debt and other long-term obligations	$ 142.0
Senior Notes | Ae Supply and Allegheny Generating Company [Member] | 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	$ 405.0
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]
Amount added to debt			88.0
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
Gain on deconsolidation, net of tax											435.0	0.0	0.0
Assumption of benefit obligations retained at FE (including Pension, OPEB and EDCP)								(820.0)			820.0
Settlement payments		$ 72.0
Amount of damages awarded to other party											66.0
Income taxes paid											52.0
Worthless stock deduction											4,800.0
Worthless stock deduction, net of tax											1,000.0
Tax consequence of outside basis difference										418.0	418.0
Nondeductible portion of interest expense											60.0	27.0
Tax benefit from excess deferred tax liabilities							$ 32.0
Impairment of assets											0.0	2,358.0	$ 10,622.0
Discontinued Operations, Disposed of by Means Other than Sale | Competitive Asset Generation Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment of assets												$ 193.0
Discontinued Operations, Disposed of by Means Other than Sale | Pleasants Power Station | FES and FENOC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment of assets									$ 120.0
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
Service Agreements and Beyond | 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										169.0
Services Agreements | 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]
Amount repaid										1.0
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										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										27.0	27.0
Purchases from related party											318.0
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								102.0
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