SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Costs for Affiliate Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Alabama Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	$ 549	$ 504	$ 478
Alabama Power | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	18	14	15
Georgia Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	762	663	639
Georgia Power | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	99	108	108
Mississippi Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	115	120	149
Mississippi Power | Alabama Power | Power Pool
Related Party Transaction [Line Items]
Costs for services	4	9	4
Southern Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	86	89	87
Southern Power | Alabama Power | Power Pool
Related Party Transaction [Line Items]
Costs for services	29	15	8
Southern Power | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	37	31	29
Southern Company Gas | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	262	239	237
Southern Company Gas | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	$ 27	$ 29	$ 29