INCOME TAXES - Changes in Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Changes in unrecognized tax benefits [Roll Forward]
Beginning balance	$ 47	$ 44	$ 0
Tax positions changes – increase from prior periods	33	3	44
Ending balance	80	47	44
Southern Company Gas
Changes in unrecognized tax benefits [Roll Forward]
Beginning balance	0	0	0
Tax positions changes – increase from prior periods	32	0	0
Ending balance	$ 32	$ 0	$ 0