DERIVATIVES - Narrative (Details) MMBTU in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) MMBTU	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	12
Estimated pre-tax gains (losses) expected to be reclassified from AOCI	$ (37,000,000)
Estimated pre-tax gains (losses) that will be reclassified from OCI to interest expense for the next 12-month period	19,000,000
Collateral already posted, aggregate fair value	62,000,000
Derivative liability	659,000,000	$ 617,000,000
Interest rate derivatives
Derivative [Line Items]
Derivative liability	52,000,000
Interest rate derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) From Derivatives Recognized in OCI	(12,000,000)	46,000,000	$ 5,000,000
Energy-related derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) From Derivatives Recognized in OCI	$ (81,000,000)	3,000,000	34,000,000
Alabama Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	3
Collateral already posted, aggregate fair value	$ 0
Derivative liability	100,000,000	15,000,000
Alabama Power | Energy-related derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) From Derivatives Recognized in OCI	$ 0
Georgia Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	4
Derivative liability	$ 113,000,000	41,000,000
Georgia Power | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) From Derivatives Recognized in OCI	$ (2,000,000)	31,000,000	0
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	$ 47,000,000	15,000,000
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) expected to be reclassified from AOCI	$ (4,000,000)
Estimated pre-tax gains (losses) that will be reclassified from OCI to interest expense for the next 12-month period	11,000,000
Collateral already posted, aggregate fair value	0
Derivative liability	27,000,000	59,000,000
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	(18,000,000)	(15,000,000)	12,000,000
Registrants | Derivative Counterparties
Derivative [Line Items]
Collateral already posted, aggregate fair value	0
Southern Company Gas
Derivative [Line Items]
Estimated pre-tax gains (losses) expected to be reclassified from AOCI	(33,000,000)
Collateral already posted, aggregate fair value	62,000,000	41,000,000
Derivative liability	87,000,000	110,000,000
Southern Company Gas | Energy-related derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) From Derivatives Recognized in OCI	$ (63,000,000)	$ 18,000,000	$ 22,000,000