DERIVATIVES - Schedule of Unrealized Gain (Loss) Recognized in the Balance Sheet (Details) - Energy-related derivatives - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	$ (257)	$ 9
Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(180)	(71)
Other regulatory assets, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(87)	(23)
Other regulatory liabilities, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	9	72
Other regulatory liabilities, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	1	31
Alabama Power
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(95)	23
Alabama Power | Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(67)	(8)
Alabama Power | Other regulatory assets, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(32)	(7)
Alabama Power | Other regulatory liabilities, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	4	29
Alabama Power | Other regulatory liabilities, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	0	9
Georgia Power
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(112)	(19)
Georgia Power | Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(80)	(26)
Georgia Power | Other regulatory assets, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(33)	(14)
Georgia Power | Other regulatory liabilities, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	0	19
Georgia Power | Other regulatory liabilities, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	1	2
Mississippi Power
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(46)	27
Mississippi Power | Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(25)	(13)
Mississippi Power | Other regulatory assets, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(22)	(2)
Mississippi Power | Other regulatory liabilities, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	1	22
Mississippi Power | Other regulatory liabilities, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	0	20
Southern Company Gas
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(4)	(22)
Southern Company Gas | Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(8)	(24)
Southern Company Gas | Other regulatory assets, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	0	0
Southern Company Gas | Other regulatory liabilities, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	4	2
Southern Company Gas | Other regulatory liabilities, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	$ 0	$ 0