COMMITMENTS, GUARANTEES AND CONTINGENCIES - Potential Collateral Obligations (Details) $ in Millions	6 Months Ended
	Jun. 30, 2023 USD ($)
Guarantor Obligations [Line Items]
Guarantor obligations	$ 208
Percent of face amount of debt	100.00%
Curing period	30 days
Upon Further Downgrade
Guarantor Obligations [Line Items]
Guarantor obligations	$ 62
Surety Bond (Collateralized Amount)
Guarantor Obligations [Line Items]
Guarantor obligations	$ 146
Percent of face amount of debt	60.00%
Capped portion of surety bond obligations	$ 39
Surety Bond (Collateralized Amount) | Pennsylvania Department of Environmental Protection
Guarantor Obligations [Line Items]
Capped portion of surety bond obligations	169
FirstEnergy
Guarantor Obligations [Line Items]
Guarantor obligations	79
FirstEnergy | Upon Further Downgrade
Guarantor Obligations [Line Items]
Guarantor obligations	0
FirstEnergy | Surety Bond (Collateralized Amount)
Guarantor Obligations [Line Items]
Guarantor obligations	79
Utilities and Transmission Companies
Guarantor Obligations [Line Items]
Guarantor obligations	129
Utilities and Transmission Companies | Upon Further Downgrade
Guarantor Obligations [Line Items]
Guarantor obligations	62
Utilities and Transmission Companies | Surety Bond (Collateralized Amount)
Guarantor Obligations [Line Items]
Guarantor obligations	$ 67