SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Costs for Affiliate Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Alabama Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	$ 611	$ 549	$ 504
Alabama Power | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	12	18	14
Georgia Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	857	762	663
Georgia Power | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	101	99	108
Mississippi Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	113	115	120
Mississippi Power | Alabama Power | Power Pool
Related Party Transaction [Line Items]
Costs for services	4	4	9
Southern Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	86	86	89
Southern Power | Alabama Power | Power Pool
Related Party Transaction [Line Items]
Costs for services	13	29	15
Southern Power | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	34	37	31
Southern Company Gas | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	261	262	239
Southern Company Gas | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	$ 28	$ 27	$ 29