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DERIVATIVES - Pre-Tax Effects of Derivatives Not Designated as Hedging (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Energy-related derivatives | Natural gas revenues |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative instruments not designated as hedging instruments, gain (loss), net | $ 0 | $ (11,000,000) | $ (117,000,000)
Energy-related derivatives | Cost of natural gas |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative instruments not designated as hedging instruments, gain (loss), net | 59,000,000 | (65,000,000) | (27,000,000)
Energy-related derivatives | Cost of natural gas | Not Designated as Hedging Instrument | Southern Company Gas |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative instruments not designated as hedging instruments, gain (loss), net | 59,000,000 | (76,000,000) | (144,000,000)
Weather derivatives |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative instruments not designated as hedging instruments, gain (loss), net | $ 15,000,000 | $ (7,000,000) | $ 0

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