FAIR VALUE MEASUREMENTS - Long-term Debt Redemption and Issuance (Details) - USD ($) $ in Millions		1 Months Ended
	May 04, 2023	May 31, 2023	Sep. 30, 2023	Mar. 31, 2023	Feb. 28, 2023	Jan. 31, 2023
Debt Instrument [Line Items]
Losses on deferred cash flows		$ 2
Losses on deferred cash flows, net		1
4.00%, 1,300 Million Notes Maturity 2026
Debt Instrument [Line Items]
Proceeds from issuance of debt	$ 1,480
Senior Notes
Debt Instrument [Line Items]
Early repayment of debt		194
Make-whole premium		34
Make-whole premium, net		27
Senior Notes | 7.375% Secured Senior Notes Maturing 2031
Debt Instrument [Line Items]
Long-term debt and other long-term obligations		$ 228
ME | Promissory Notes | 3.50% Series B Senior Notes Due 2023
Debt Instrument [Line Items]
Issuance interest rate				3.50%
Face amount of debt				$ 300
ME | Promissory Notes | 3.50% Series B Senior Notes Due 2023 | Revolving Credit Facility
Debt Instrument [Line Items]
Issuance interest rate				3.50%
Face amount of debt				$ 300
ME | Promissory Notes | 5.20%, 425 Million Notes Maturing 2028
Debt Instrument [Line Items]
Issuance interest rate				5.20%
Face amount of debt				$ 425
FE | Promissory Notes | 7.375% Secured Senior Notes Maturing 2031
Debt Instrument [Line Items]
Issuance interest rate		7.375%
Face amount of debt		$ 194
FE | Promissory Notes | 4.00%, 1,300 Million Notes Maturity 2026
Debt Instrument [Line Items]
Issuance interest rate		4.00%
Face amount of debt	$ 1,500	$ 1,500
WP | First Mortgage Bond | 5.29%, 50 Million Notes Maturing 2023
Debt Instrument [Line Items]
Issuance interest rate						5.29%
Face amount of debt						$ 50
MAIT | Promissory Notes | 5.39%, 175 Million Notes Maturing 2023
Debt Instrument [Line Items]
Issuance interest rate					5.39%
Face amount of debt					$ 175
PN | Promissory Notes | 5.15%, 300 Million Notes Maturing 2026
Debt Instrument [Line Items]
Issuance interest rate				5.15%
Face amount of debt				$ 300
ATSI | Promissory Notes | 5.13%, 150 Million Notes Maturity 2033
Debt Instrument [Line Items]
Issuance interest rate		5.13%
Face amount of debt		$ 150
PE | First Mortgage Bond | 5.64%, $100 Million Notes Maturity 2028
Debt Instrument [Line Items]
Issuance interest rate			5.64%
Face amount of debt			$ 100
PE | First Mortgage Bond | 5.37%, $50 Million Notes Maturity 2030
Debt Instrument [Line Items]
Issuance interest rate			5.73%
Face amount of debt			$ 50
MP | Promissory Notes | 4.1% Notes, 400 Million Notes Maturing 2023 | Revolving Credit Facility
Debt Instrument [Line Items]
Issuance interest rate			4.10%
Face amount of debt			$ 400
MP | First Mortgage Bond | 5.85%, $400 Million Notes Maturity 2034
Debt Instrument [Line Items]
Issuance interest rate			5.85%
Face amount of debt			$ 400