Pension and Other Postemployment Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Pensions
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service costs	$ 49	$ 40
Interest costs	93	97
Expected return on plan assets	(125)	(121)
Amortization of prior service cost (credit)	3	3
Net periodic cost (credits)	20	19
OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service costs	3	3
Interest costs	9	12
Expected return on plan assets	(8)	(9)
Amortization of prior service cost (credit)	(50)	(51)
Net periodic cost (credits)	(46)	(45)
FirstEnergy | Pensions
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic cost (credits)	11	13
FirstEnergy | OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic cost (credits)	(30)	(30)
FES | Pensions
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic cost (credits)	3	3
FES | OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic cost (credits)	$ (3)	$ (4)