INCOME TAXES - Changes in Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Changes in unrecognized tax benefits [Roll Forward]
Beginning balance	$ 80	$ 47	$ 44
Increase from prior periods	88	33	3
Ending balance	116	80	47
Estimated loss on plants under construction
Changes in unrecognized tax benefits [Roll Forward]
Statute of limitations expiration	(52)
Georgia Power
Changes in unrecognized tax benefits [Roll Forward]
Beginning balance	0	0	0
Increase from prior periods	86	0	0
Ending balance	77	0	0
Georgia Power | Estimated loss on plants under construction
Changes in unrecognized tax benefits [Roll Forward]
Statute of limitations expiration	(9)
Southern Company Gas
Changes in unrecognized tax benefits [Roll Forward]
Beginning balance	32	0	0
Increase from prior periods	2	32	0
Ending balance	34	$ 32	$ 0
Southern Company Gas | Estimated loss on plants under construction
Changes in unrecognized tax benefits [Roll Forward]
Statute of limitations expiration	$ 0