FAIR VALUE MEASUREMENTS - Long-term Debt Redemption and Issuance (Details) - USD ($) $ in Millions	1 Months Ended
Mar. 31, 2024	Apr. 30, 2024
Senior Notes
Debt Instrument [Line Items]
Unamortized debt issuance expense	$ 1
7.375% Secured Senior Notes Maturing 2031 \| Promissory Notes \| FE
Debt Instrument [Line Items]
Issuance interest rate		7.375%
Face amount of debt	463	$ 463
Make-whole premium	80
Make-whole premium, net	63
Losses on deferred cash flows	4
Losses on deferred cash flows, net	$ 3
4.70% Secured Senior Notes Maturing 2024 \| Promissory Notes \| CEI
Debt Instrument [Line Items]
Issuance interest rate		4.70%
Face amount of debt		$ 500
4.10% Secured Senior Notes Maturing 2024 \| Promissory Notes \| ATSI
Debt Instrument [Line Items]
Issuance interest rate		4.10%
Face amount of debt		$ 400
5.63% Secured Senior Notes Maturing 2034 \| First Mortgage Bond \| ATSI
Debt Instrument [Line Items]
Issuance interest rate	5.63%
Face amount of debt	$ 150
5.94% Secured Senior Notes Maturing 2031 \| Promissory Notes \| MAIT
Debt Instrument [Line Items]
Issuance interest rate		5.94%
Face amount of debt		$ 250

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