Organization, Basis of Presentation and Significant Accounting Policies (Details 2) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of Basic and Diluted Earnings per Share of Common Stock
Income (loss) from continuing operations	$ (306)	$ 333	$ 64	$ 122	$ 142	$ 209	$ (168)	$ 192	$ 213	$ 375	$ 755
Less: Income attributable to noncontrolling interest									0	0	1
Income from continuing operations available to common shareholders									213	375	754
Discontinued operations (net of income taxes of $69, $9 and $8, respectively) (Note 19)	0	0	0	86	0	9	4	4	86	17	16
EARNINGS AVAILABLE TO FIRSTENERGY CORP.									$ 299us-gaap_NetIncomeLoss	$ 392us-gaap_NetIncomeLoss	$ 770us-gaap_NetIncomeLoss
Weighted average number of basic shares outstanding									420	418	418
Assumed exercise of dilutive stock options and awards (in shares)									1	1	1
Weighted average number of diluted shares outstanding									421	419	419
Earnings per share:
Basic - Continuing Operations, in dollars per share	$ (0.73)	$ 0.79	$ 0.16	$ 0.29	$ 0.34	$ 0.50	$ (0.40)	$ 0.46	$ 0.51	$ 0.90	$ 1.81
Basic - Discontinued Operations, in dollars per share	$ 0.00	$ 0.00	$ 0.00	$ 0.21	$ 0.00	$ 0.02	$ 0.01	$ 0.01	$ 0.20	$ 0.04	$ 0.04
Basic - Earnings Available to FirstEnergy Corp., in dollars per share	$ (0.73)us-gaap_EarningsPerShareBasic	$ 0.79us-gaap_EarningsPerShareBasic	$ 0.16us-gaap_EarningsPerShareBasic	$ 0.50us-gaap_EarningsPerShareBasic	$ 0.34us-gaap_EarningsPerShareBasic	$ 0.52us-gaap_EarningsPerShareBasic	$ (0.39)us-gaap_EarningsPerShareBasic	$ 0.47us-gaap_EarningsPerShareBasic	$ 0.71us-gaap_EarningsPerShareBasic	$ 0.94us-gaap_EarningsPerShareBasic	$ 1.85us-gaap_EarningsPerShareBasic
Diluted earnings per share:
Diluted - Continuing Operations, in dollars per share	$ (0.73)	$ 0.79	$ 0.15	$ 0.29	$ 0.34	$ 0.50	$ (0.40)	$ 0.46	$ 0.51	$ 0.90	$ 1.80
Diluted - Discontinued Operations, in dollars per share	$ 0.00	$ 0.00	$ 0.00	$ 0.20	$ 0.00	$ 0.02	$ 0.01	$ 0.01	$ 0.20	$ 0.04	$ 0.04
Diluted - Earnings Available to FirstEnergy Corp., in dollars per share	$ (0.73)us-gaap_EarningsPerShareDiluted	$ 0.79us-gaap_EarningsPerShareDiluted	$ 0.15us-gaap_EarningsPerShareDiluted	$ 0.49us-gaap_EarningsPerShareDiluted	$ 0.34us-gaap_EarningsPerShareDiluted	$ 0.52us-gaap_EarningsPerShareDiluted	$ (0.39)us-gaap_EarningsPerShareDiluted	$ 0.47us-gaap_EarningsPerShareDiluted	$ 0.71us-gaap_EarningsPerShareDiluted	$ 0.94us-gaap_EarningsPerShareDiluted	$ 1.84us-gaap_EarningsPerShareDiluted
Shares excluded from the calculation of diluted shares outstanding, in shares									2	2	0

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