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, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Reconciliation of Basic and Diluted Earnings per Share of Common Stock
Weighted average number of basic shares outstanding									418		399		304
Assumed exercise of dilutive stock options and awards									1	[1]	2	[1]	1	[1]
Weighted average number of diluted shares outstanding									419		401		305
Earnings available to FirstEnergy Corp.	$ (148)	$ 425	$ 187	$ 306	$ 98	$ 532	$ 203	$ 52	$ 770		$ 885		$ 742
Basic earnings per share of common stock (in dollars per share)	$ (0.35)	$ 1.02	$ 0.45	$ 0.73	$ 0.23	$ 1.27	$ 0.48	$ 0.15	$ 1.85		$ 2.22		$ 2.44
Diluted earnings per share of common stock (in dollars per share)	$ (0.35)	$ 1.01	$ 0.45	$ 0.73	$ 0.23	$ 1.27	$ 0.48	$ 0.15	$ 1.84		$ 2.21		$ 2.42

[1] The number of potentially dilutive securities not included in the calculation of diluted shares outstanding due to their antidilutive effect were not significant for the years ending December 31, 2012, 2011 or 2010.