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