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CONTINGENCIES, COMMITMENTS, AND GUARANTEES - SO Litigation (Details) - Kemper County energy facility assets, net - Mississippi Power - USD ($) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2018 | Dec. 31, 2016 | Dec. 31, 2010
Loss Contingencies [Line Items] |  |  |
Government grants expected |  | $ 137 | $ 270
Government grants received | $ 387 |  |

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