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ORGANIZATION AND BASIS OF PRESENTATION - Summary of Changes in Goodwill (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Goodwill [Line Items] |  |
Goodwill | $ 5,618 | $ 5,618
Utilities and FET |  |
Goodwill [Line Items] |  |
Goodwill | 5,004 |
Regulated Transmission |  |
Goodwill [Line Items] |  |
Goodwill | $ 614 |

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