SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Costs for Affiliate Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Alabama Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	$ 855	$ 813	$ 611
Alabama Power | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	11	13	12
Georgia Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	1,364	1,197	857
Georgia Power | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	105	103	101
Mississippi Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	138	130	113
Mississippi Power | Alabama Power | Power Pool
Related Party Transaction [Line Items]
Costs for services	19	8	4
Southern Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	101	93	86
Southern Power | Alabama Power | Power Pool
Related Party Transaction [Line Items]
Costs for services	41	17	13
Southern Power | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	31	35	34
Southern Company Gas | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	313	290	261
Southern Company Gas | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	$ 29	$ 28	$ 28