Organization and Basis of Presentation (Details) customer in Millions	3 Months Ended			6 Months Ended		9 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($) transmission_center company MW	Mar. 31, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) customer transmission_center company mi MW	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) MW	Dec. 31, 2018 USD ($) MW	Apr. 11, 2019 USD ($)	Jan. 01, 2019 USD ($)	Sep. 26, 2018 USD ($)	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										$ 225,000,000
Capitalized cost of equity	$ 9,000,000		$ 12,000,000	$ 22,000,000	$ 23,000,000
Capitalized interest	7,000,000		4,000,000	12,000,000	8,000,000
Total assets	$ 40,884,000,000			$ 40,884,000,000		$ 40,063,000,000	$ 40,063,000,000
Accounting Standards Update 2016-02
Property, Plant and Equipment [Line Items]
Total assets									$ 186,000,000
Total liabilities									$ 186,000,000
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
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
Terms of settlement agreement							66,000,000
Estimated tax payments that have been made							$ 52,000,000
Income (Loss) from discontinued operations, before tax	$ 0		$ (25,000,000)	$ 3,000,000	$ (28,000,000)
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										71,000,000
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										88,000,000
Loans Payable | Intercompany Income Tax Allocation Agreement | FES
Property, Plant and Equipment [Line Items]
Face amount of debt										628,000,000
Line of Credit | Secured Credit Facility | FES
Property, Plant and Equipment [Line Items]
Maximum amount borrowed under revolving credit facility										500,000,000
Line of Credit | Credit Agreement | FES
Property, Plant and Equipment [Line Items]
Maximum amount borrowed under revolving credit facility										$ 200,000,000
Pleasants Power Station | Purchase Agreement with Subsidiary of LS Power | AE Supply
Property, Plant and Equipment [Line Items]
Plant capacity (in MW's) | MW	1,300			1,300		1,300	1,300
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	$ 67,000,000			$ 101,000,000		$ 112,500,000
Affiliated Companies | Pension Plan Enhancement | Discontinued Operations, Disposed of by Means Other than Sale | FES and FENOC
Property, Plant and Equipment [Line Items]
Amounts of transaction				14,000,000
Affiliated Companies | Benefit Obligations | Discontinued Operations, Disposed of by Means Other than Sale | FES and FENOC
Property, Plant and Equipment [Line Items]
Obligations settled in cash								$ 60,000,000
Total obligations to be settled								$ 87,000,000
Income (Loss) from discontinued operations, before tax		$ 27,000,000
Affiliated Companies | Benefit Obligations | Discontinued Operations, Disposed of by Means Other than Sale | FES and FENOC | FES
Property, Plant and Equipment [Line Items]
Amounts of transaction	$ 9,000,000			$ 19,000,000
Continuing Operations | Affiliated Companies | Benefit Obligations | Discontinued Operations, Disposed of by Means Other than Sale | FES and FENOC
Property, Plant and Equipment [Line Items]
Income (Loss) from discontinued operations, before tax		$ 17,000,000