SEGMENT INFORMATION - Narrative (Details) mi² in Thousands, customer in Millions, $ in Millions		3 Months Ended	12 Months Ended
	Apr. 30, 2022 USD ($)	Dec. 31, 2021 USD ($) mi² company MW	Dec. 31, 2021 USD ($) mi² company customer MW	Dec. 31, 2020 USD ($)
FET | North American Transmission Company II LLC | Forecast
Segment Reporting Information [Line Items]
Sale of ownership interest by parent	19.90%
Sale of ownership interest by parent	$ 2,375
Regulated Distribution
Segment Reporting Information [Line Items]
Number of existing utility operating companies | company		10	10
Number of customers served by utility operating companies | customer			6
Number of square miles in service area | mi²		65	65
Megawatts of net demonstrated capacity of competitive segment (in MW's) | MW		3,580	3,580
Regulated Distribution | Disposal Group, Held-for-sale | Yard Creek Generating Facility
Segment Reporting Information [Line Items]
Assets held-for-sale				$ 45
Regulated Distribution | Disposal Group, Disposed of by Sale | TMI-2
Segment Reporting Information [Line Items]
Gain on disposal of discontinued operation, net of tax		$ 33
Other/Corporate | OVEC
Segment Reporting Information [Line Items]
Megawatts of net demonstrated capacity of competitive segment (in MW's) | MW		67	67
FE | Other/Corporate
Segment Reporting Information [Line Items]
Long-term debt and other long-term obligations		$ 7,900	$ 7,900