Pension and Other Postemployment Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Pensions
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service costs	$ 49	$ 40	$ 147	$ 120
Interest costs	93	97	279	291
Expected return on plan assets	(125)	(121)	(375)	(363)
Amortization of prior service cost (credit)	3	3	9	9
Net periodic cost (credits)	20	19	60	57
OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service costs	3	3	9	9
Interest costs	9	12	27	36
Expected return on plan assets	(8)	(9)	(24)	(27)
Amortization of prior service cost (credit)	(50)	(50)	(157)	(152)
Net periodic cost (credits)	(46)	(44)	(145)	(134)
FirstEnergy | Pensions
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic cost (credits)	16	14	41	41
FirstEnergy | OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic cost (credits)	(31)	(30)	(95)	(92)
FES | Pensions
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic cost (credits)	5	5	13	13
FES | OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic cost (credits)	$ (4)	$ (4)	$ (12)	$ (12)