DERIVATIVES - Narrative (Details) MMBTU in Millions	12 Months Ended
	Dec. 31, 2025 USD ($) MMBTU	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	15
Collateral already posted, aggregate fair value	$ 33,000,000	$ 17,000,000
Derivative liability	267,000,000	554,000,000
Interest rate derivatives
Derivative [Line Items]
Derivative liability	20,000,000
Interest rate derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) From Derivatives Recognized in OCI	6,000,000	23,000,000	$ (12,000,000)
Energy-related derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) From Derivatives Recognized in OCI	$ (8,000,000)	(7,000,000)	(81,000,000)
Alabama Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	4
Collateral already posted, aggregate fair value	$ 0
Derivative liability	$ 18,000,000	23,000,000
Georgia Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	6
Derivative liability	$ 19,000,000	27,000,000
Georgia Power | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) From Derivatives Recognized in OCI	$ 4,000,000	24,000,000	(2,000,000)
Mississippi Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	2
Derivative liability	$ 14,000,000	17,000,000
Mississippi Power | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) From Derivatives Recognized in OCI	$ (1,000,000)	7,000,000	0
Southern Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	3
Estimated pre-tax gains (losses) that will be reclassified from OCI to interest expense for the next 12-month period	$ 17,000,000
Collateral already posted, aggregate fair value	0
Derivative liability	1,000,000	51,000,000
Southern Power | Interest rate derivatives
Derivative [Line Items]
Derivative liability	0
Southern Power | Energy-related derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) From Derivatives Recognized in OCI	(1,000,000)	(1,000,000)	(18,000,000)
Registrants | Derivative Counterparties
Derivative [Line Items]
Collateral already posted, aggregate fair value	0
Southern Company Gas
Derivative [Line Items]
Collateral already posted, aggregate fair value	33,000,000	17,000,000
Derivative liability	65,000,000	84,000,000
Southern Company Gas | Interest rate derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) From Derivatives Recognized in OCI	2,000,000	(5,000,000)	0
Southern Company Gas | Energy-related derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) From Derivatives Recognized in OCI	(6,000,000)	$ (6,000,000)	$ (63,000,000)
Traditional Electric Operating Companies
Derivative [Line Items]
Estimated pre-tax gains (losses) that will be reclassified from OCI to interest expense for the next 12-month period	$ 0