INCOME TAXES - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended
	Apr. 30, 2023	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2024	Mar. 31, 2023	May 31, 2022
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred tax assets valuation allowance, amount		$ 65
Unrecognized tax benefits, increase resulting from settlements with taxing authorities		64
Uncertain tax positions		50		$ 2	$ 50	$ 2
Deferred tax assets		4			4			$ 9
Deferred tax assets, expected to be refunded to customers		4			4
Operating loss carryforwards, not subject to expiration, net of tax		$ 1,000			$ 1,000
Estimated AMT paid	$ 49
Disposition of business, amount			$ 752
North American Transmission Company II LLC | FET
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Sale of ownership interest by parent									19.90%
North American Transmission Company II LLC | Forecast | FET
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Sale of ownership interest by parent							30.00%
Equity interest rate of combined sale							30.00%