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Derivatives - Narrative (Details) MMBTU in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2025 USD ($) | Sep. 30, 2024 USD ($) | Sep. 30, 2025 USD ($) MMBTU | Sep. 30, 2024 USD ($) | Dec. 31, 2024 USD ($)
Derivative [Line Items] |  |  |  |  |
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU |  |  | 1.5 |  |
Energy-related derivative hedge gain (loss) to be reclassified within twelve months | $ 0 |  | $ 0 |  |
Gain (Loss) Recognized in OCI on Derivatives | (18,000,000) | $ (2,000,000) | 48,000,000 | $ (7,000,000) |
Collateral already posted, assets, aggregate fair value | 10,000,000 |  | 10,000,000 |  |
Derivatives | 238,000,000 |  | 238,000,000 |  | $ 554,000,000
Interest rate derivatives |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivatives | 20,000,000 |  | 20,000,000 |  |
Interest rate derivatives | Cash Flow Hedging |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Gain (Loss) Recognized in OCI on Derivatives | (1,000,000) | (8,000,000) | 6,000,000 | 16,000,000 |
Interest rate derivatives | Cash Flow Hedging | Interest Expense |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Gain (loss) on hedges | (4,000,000) | (4,000,000) | (10,000,000) | (12,000,000) |
Interest rate derivatives | Fair Value Hedging | Interest Expense |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Gain (loss) on hedges | 16,000,000 | 78,000,000 | 85,000,000 | 47,000,000 |
Energy-related derivatives | Energy-related derivatives not designated as hedging instruments | Cost of Natural Gas |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative instruments not designated as hedging instruments, gain (loss), net | (1,000,000) | 6,000,000 | (7,000,000) | 69,000,000 |
Energy-related derivatives | Cash Flow Hedging |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Gain (Loss) Recognized in OCI on Derivatives | (12,000,000) | (7,000,000) | (6,000,000) | (11,000,000) |
Foreign currency derivatives | Cash Flow Hedging |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Gain (Loss) Recognized in OCI on Derivatives | (6,000,000) | 15,000,000 | 60,000,000 | (4,000,000) |
Foreign currency derivatives | Cash Flow Hedging | Interest Expense |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Gain (loss) on hedges | (2,000,000) | (3,000,000) | $ (8,000,000) | (9,000,000) |
ALABAMA POWER CO |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU |  |  | 0.4 |  |
Collateral already posted, assets, aggregate fair value | 0 |  | $ 0 |  |
Derivatives | 8,000,000 |  | 8,000,000 |  | 23,000,000
ALABAMA POWER CO | Interest rate derivatives |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Cash flow hedge gain (loss) to be reclassified within twelve months | 0 |  | $ 0 |  |
GEORGIA POWER CO |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU |  |  | 0.6 |  |
Derivatives | 8,000,000 |  | $ 8,000,000 |  | 27,000,000
GEORGIA POWER CO | Interest rate derivatives |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Cash flow hedge gain (loss) to be reclassified within twelve months | 0 |  | 0 |  |
GEORGIA POWER CO | Interest rate derivatives | Cash Flow Hedging |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Gain (Loss) Recognized in OCI on Derivatives | 0 | 1,000,000 | $ 3,000,000 | 17,000,000 |
MISSISSIPPI POWER CO |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU |  |  | 0.2 |  |
Derivatives | 8,000,000 |  | $ 8,000,000 |  | 17,000,000
MISSISSIPPI POWER CO | Interest rate derivatives |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Cash flow hedge gain (loss) to be reclassified within twelve months | 0 |  | 0 |  |
MISSISSIPPI POWER CO | Interest rate derivatives | Cash Flow Hedging |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Gain (Loss) Recognized in OCI on Derivatives | 0 | 0 | $ 0 | 7,000,000 |
SOUTHERN POWER CO |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU |  |  | 0.3 |  |
Energy-related derivative hedge gain (loss) to be reclassified within twelve months | 0 |  | $ 0 |  |
Foreign currency cash flow hedge gain (loss) to be reclassified during next 12 months | 20,000,000 |  | 20,000,000 |  |
Gain (Loss) Recognized in OCI on Derivatives | (8,000,000) | 13,000,000 | 60,000,000 | (6,000,000) |
Collateral already posted, assets, aggregate fair value | 0 |  | 0 |  |
Derivatives | 1,000,000 |  | 1,000,000 |  | 51,000,000
SOUTHERN POWER CO | Interest rate derivatives |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Cash flow hedge gain (loss) to be reclassified within twelve months | 0 |  | 0 |  |
SOUTHERN POWER CO | Energy-related derivatives |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivatives | 0 |  | 0 |  |
SOUTHERN POWER CO | Energy-related derivatives | Cash Flow Hedging |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Gain (Loss) Recognized in OCI on Derivatives | (2,000,000) | (2,000,000) | 0 | (2,000,000) |
SOUTHERN POWER CO | Foreign currency derivatives | Cash Flow Hedging |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Gain (Loss) Recognized in OCI on Derivatives | (6,000,000) | 15,000,000 | 60,000,000 | (4,000,000) |
SOUTHERN POWER CO | Foreign currency derivatives | Cash Flow Hedging | Interest Expense |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Gain (loss) on hedges | (2,000,000) | (3,000,000) | (8,000,000) | (9,000,000) |
Registrants | Derivative Counterparties |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Collateral already posted, assets, aggregate fair value | 0 |  | 0 |  |
SOUTHERN Co GAS |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Energy-related derivative hedge gain (loss) to be reclassified within twelve months | 0 |  | 0 |  |
Gain (Loss) Recognized in OCI on Derivatives | (11,000,000) | (10,000,000) | (3,000,000) | (14,000,000) |
Collateral already posted, assets, aggregate fair value | 10,000,000 |  | 10,000,000 |  | 17,000,000
Derivatives | 57,000,000 |  | 57,000,000 |  | $ 84,000,000
SOUTHERN Co GAS | Interest rate derivatives |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Cash flow hedge gain (loss) to be reclassified within twelve months | 0 |  | 0 |  |
SOUTHERN Co GAS | Interest rate derivatives | Cash Flow Hedging |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Gain (Loss) Recognized in OCI on Derivatives | (1,000,000) | (6,000,000) | 3,000,000 | (5,000,000) |
SOUTHERN Co GAS | Interest rate derivatives | Cash Flow Hedging | Interest Expense |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Gain (loss) on hedges | 0 | 0 | (1,000,000) | 0 |
SOUTHERN Co GAS | Interest rate derivatives | Fair Value Hedging | Interest Expense |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Gain (loss) on hedges | 7,000,000 | 28,000,000 | 28,000,000 | 18,000,000 |
SOUTHERN Co GAS | Energy-related derivatives | Cash Flow Hedging |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Gain (Loss) Recognized in OCI on Derivatives | (10,000,000) | $ (4,000,000) | (6,000,000) | $ (9,000,000) |
Traditional Electric Operating Companies | Energy-related derivatives |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivatives | $ 0 |  | $ 0 |  |

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