SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Affiliate Transactions (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Southern Nuclear Operating Company, Inc. | Alabama Power
Related Party Transaction [Line Items]
Costs for services	$ 275	$ 260	$ 251
Southern Nuclear Operating Company, Inc. | Georgia Power
Related Party Transaction [Line Items]
Costs for services	832	835	899
PowerSecure | Alabama Power | Equipment Purchase And Service Agreements
Related Party Transaction [Line Items]
Costs for services	0	0	0
PowerSecure | Georgia Power | Equipment Purchase And Service Agreements
Related Party Transaction [Line Items]
Costs for services	51	20	5
PowerSecure | Southern Company Gas | US General Services Administration
Related Party Transaction [Line Items]
Costs for services	1	13	29
Contract amount	74
PowerSecure | Mississippi Power | Equipment Purchase And Service Agreements
Related Party Transaction [Line Items]
Costs for services	0	0	0
Southern Company Services, Inc. | Alabama Power
Related Party Transaction [Line Items]
Costs for services	855	813	611
Southern Company Services, Inc. | Georgia Power
Related Party Transaction [Line Items]
Costs for services	1,364	1,197	857
Southern Company Services, Inc. | Southern Power
Related Party Transaction [Line Items]
Costs for services	101	93	86
Southern Company Services, Inc. | Southern Company Gas
Related Party Transaction [Line Items]
Costs for services	313	290	261
Southern Company Services, Inc. | Mississippi Power
Related Party Transaction [Line Items]
Costs for services	138	130	113
Non-Fuel Expense | Mississippi Power | Alabama Power
Related Party Transaction [Line Items]
Costs for services	9	7	5
Electric Transmission | Southern Company Services, Inc. | Southern Power
Related Party Transaction [Line Items]
Costs for services	$ 9	$ 25	$ 33