ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 10,166
Income tax on other comprehensive income	(1)	$ (1)	$ (3)
Other comprehensive income, net of tax	(3)	1	(10)
Ending balance	10,437	10,166
Gains & Losses on Cash Flow
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0	(7)	(8)
Amounts reclassified from AOCI	2	9	1
Income tax on other comprehensive income	0	2	0
Other comprehensive income, net of tax	2	7	1
Ending balance	2	0	(7)
Defined Benefit Pension & OPEB Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(14)	(8)	3
Amounts reclassified from AOCI	(6)	(9)	(14)
Income tax on other comprehensive income	(1)	(3)	(3)
Other comprehensive income, net of tax	(5)	(6)	(11)
Ending balance	(19)	(14)	(8)
Total FirstEnergy Corp. AOCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(14)	(15)	(5)
Other comprehensive income, net of tax	(3)	1	(10)
Ending balance	$ (17)	$ (14)	$ (15)