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Pension and Other Postemployment Benefits (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Dec. 31, 2016
Pension      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Service costs $ 52 $ 48  
Interest costs 97 100  
Expected return on plan assets (112) (97)  
Amortization of prior service costs (credits) 2 2  
Net periodic costs (credits) 39 53  
OPEB      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Service costs 1 1  
Interest costs 7 7  
Expected return on plan assets (8) (8)  
Amortization of prior service costs (credits) (20) (20)  
Net periodic costs (credits) (20) (20)  
FirstEnergy | Pension      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Net periodic benefit expense (credit) 32 37  
FirstEnergy | OPEB      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Net periodic benefit expense (credit) (15) (15)  
FES      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Non-current liabilities 866   $ 866
FES | Pension      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Net periodic costs (credits) 3 6  
Net periodic benefit expense (credit) 3 6  
FES | OPEB      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Net periodic costs (credits) (4) (4)  
Net periodic benefit expense (credit) (4) $ (4)  
FENOC      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Non-current liabilities $ 570   $ 570