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Consolidated Statements of Income (Loss) (FirstEnergy Corp.) (Parenthetical) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Income Statement [Abstract]        
Excise taxes collected $ 102 $ 111 $ 293 $ 310