Pension and Other Postemployment Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Pensions
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service costs	$ 49	$ 40	$ 98	$ 80
Interest costs	93	97	186	194
Expected return on plan assets	(125)	(121)	(250)	(242)
Amortization of prior service cost (credit)	3	3	6	6
Net periodic cost (credits)	20	19	40	38
OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service costs	3	3	6	6
Interest costs	9	12	18	24
Expected return on plan assets	(8)	(9)	(16)	(18)
Amortization of prior service cost (credit)	(58)	(51)	(107)	(102)
Net periodic cost (credits)	(54)	(45)	(99)	(90)
FirstEnergy | Pensions
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic cost (credits)	14	14	25	27
FirstEnergy | OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic cost (credits)	(34)	(32)	(64)	(62)
FES | Pensions
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic cost (credits)	5	5	8	8
FES | OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic cost (credits)	$ (5)	$ (4)	$ (8)	$ (8)