SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Affiliate Transactions (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Southern Nuclear Operating Company, Inc. | Alabama Power
Related Party Transaction [Line Items]
Costs for services	$ 260	$ 251	$ 267
Southern Nuclear Operating Company, Inc. | Georgia Power
Related Party Transaction [Line Items]
Costs for services	835	899	895
Southern Power | Georgia Power
Related Party Transaction [Line Items]
Costs for services	203	143	151
PowerSecure | Southern Company Gas | US General Services Administration
Related Party Transaction [Line Items]
Costs for services	13	29	10
Contract amount			74
Southern Company Services, Inc. | Alabama Power
Related Party Transaction [Line Items]
Costs for services	813	611	549
Southern Company Services, Inc. | Georgia Power
Related Party Transaction [Line Items]
Costs for services	1,197	857	762
Southern Company Services, Inc. | Southern Power
Related Party Transaction [Line Items]
Costs for services	93	86	86
Southern Company Services, Inc. | Southern Company Gas
Related Party Transaction [Line Items]
Costs for services	290	261	262
Southern Company Services, Inc. | Mississippi Power
Related Party Transaction [Line Items]
Costs for services	130	113	115
Non-Fuel Expense | Mississippi Power | Alabama Power
Related Party Transaction [Line Items]
Costs for services	7	5	6
Purchased Power from Affiliates | Southern Power
Related Party Transaction [Line Items]
Costs for services	149	145	154
Operating Lease PPA | Southern Power
Related Party Transaction [Line Items]
Costs for services	121	116	116
Operating Lease PPA | Mississippi Power
Related Party Transaction [Line Items]
Costs for services	60
Electric Transmission | Southern Company Services, Inc. | Southern Power
Related Party Transaction [Line Items]
Costs for services	$ 25	$ 33	$ 39