Consolidated Statements of Common Stockholders' Equity (FirstEnergy Corp.) - USD ($) $ in Millions		Total	Common Stock	OPIC	AOCI	Accumulated Deficit	Series A Convertible Preferred Stock
Beginning Balance (in shares) at Dec. 31, 2017			445,000,000				0
Beginning Balance at Dec. 31, 2017		$ 3,925	$ 44	$ 10,001	$ 142	$ (6,262)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
NET INCOME		1,348				1,348
Other comprehensive loss, net of tax		(101)			(101)
Stock-based compensation		60		60
Cash dividends declared on common stock		(906)		(906)
Cash dividends declared on preferred stock		(71)		(71)
Stock Investment Plan and certain share-based benefit plans (in shares)			4,000,000
Stock Investment Plan and certain share-based benefit plans		62	$ 1	61
Stock issuance (Note 11) (in shares)	[1]		30,000,000				1,600,000
Stock issuance (Note 11)	[1]	2,462	$ 3	2,297			$ 162
Conversion of Series A Convertible Stock (Note 11) (in shares)			33,000,000				(900,000)
Conversion of Series A Convertible Stock		0	$ 3	88			$ (91)
Ending Balance (in shares) at Dec. 31, 2018			512,000,000				700,000
Ending Balance at Dec. 31, 2018		6,814	$ 51	11,530	41	(4,879)	$ 71
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of adopting new accounting pronouncements		35				35
NET INCOME		912				912
Other comprehensive loss, net of tax		(21)			(21)
Stock-based compensation		41		41
Cash dividends declared on common stock		(824)		(824)
Cash dividends declared on preferred stock		(3)		(3)
Stock Investment Plan and certain share-based benefit plans (in shares)			3,000,000
Stock Investment Plan and certain share-based benefit plans		56		56
Conversion of Series A Convertible Stock (Note 11) (in shares)			26,000,000				(700,000)
Conversion of Series A Convertible Stock		$ 0	$ 3	68			$ (71)
Ending Balance (in shares) at Dec. 31, 2019		540,652,222	541,000,000				0
Ending Balance at Dec. 31, 2019		$ 6,975	$ 54	10,868	20	(3,967)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of adopting new accounting pronouncements		6,975
NET INCOME		1,079				1,079
Other comprehensive loss, net of tax		(25)			(25)
Stock-based compensation		26		26
Cash dividends declared on common stock		(846)		(846)
Stock Investment Plan and certain share-based benefit plans (in shares)			2,000,000
Stock Investment Plan and certain share-based benefit plans		$ 28		28
Ending Balance (in shares) at Dec. 31, 2020		543,117,533	543,000,000				0
Ending Balance at Dec. 31, 2020		$ 7,237	$ 54	$ 10,076	$ (5)	$ (2,888)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of adopting new accounting pronouncements		$ 7,237

[1] The Preferred Stock included an embedded conversion option at a price that is below the fair value of the Common Stock on the commitment date. This BCF, which was approximately $296 million, was recorded to OPIC as well as the amortization of the BCF (deemed dividend) through the period from the issue date to the first allowable conversion date (July 22, 2018) and as such there is no net impact to OPIC for the year ended December 31, 2018.