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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% |  |

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