Pension and Other Postemployment Benefits (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Jan. 31, 2018	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Additional funding contributions	$ 750
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service costs		$ 56	$ 52
Interest costs		93	97
Expected return on plan assets		(144)	(112)
Amortization of prior service costs (credits)		2	2
Net periodic costs (credits)		7	39
Pension | FES and FENOC | Discontinued Operations, Disposed of by Means Other than Sale
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic costs (credits)		13	16
OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service costs		1	1
Interest costs		6	7
Expected return on plan assets		(8)	(8)
Amortization of prior service costs (credits)		(20)	(20)
Net periodic costs (credits)		(21)	(20)
OPEB | FES and FENOC | Discontinued Operations, Disposed of by Means Other than Sale
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic costs (credits)		(10)	(8)
FirstEnergy | Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit expense (credit)		(14)	32
FirstEnergy | OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit expense (credit)		$ (21)	$ (15)
Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions by employer	$ 500