SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Costs for Affiliate Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Alabama Power \| Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	$ 813	$ 611	$ 549
Alabama Power \| Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	13	12	18
Georgia Power \| Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	1,197	857	762
Georgia Power \| Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	103	101	99
Mississippi Power \| Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	130	113	115
Mississippi Power \| Alabama Power \| Power Pool
Related Party Transaction [Line Items]
Costs for services	8	4	4
Southern Power \| Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	93	86	86
Southern Power \| Alabama Power \| Power Pool
Related Party Transaction [Line Items]
Costs for services	17	13	29
Southern Power \| Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	35	34	37
Southern Company Gas \| Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	290	261	262
Southern Company Gas \| Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	$ 28	$ 28	$ 27