SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 748	$ 1,917
Restricted cash:
Total cash, cash equivalents, and restricted cash	921	2,037	$ 1,829	$ 1,068
Other current assets
Restricted cash:
Restricted cash	141	62
Other deferred charges and assets
Restricted cash:
Restricted cash	31	58
Alabama Power
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	324	687
Restricted cash:
Total cash, cash equivalents, and restricted cash	409	687	1,060	530
Alabama Power | Other current assets
Restricted cash:
Restricted cash	85	0
Alabama Power | Other deferred charges and assets
Restricted cash:
Restricted cash	0	0
Georgia Power
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	9	364
Restricted cash:
Total cash, cash equivalents, and restricted cash	75	480	33	9
Georgia Power | Other current assets
Restricted cash:
Restricted cash	37	60
Georgia Power | Other deferred charges and assets
Restricted cash:
Restricted cash	29	56
Southern Power
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	124	131
Restricted cash:
Total cash, cash equivalents, and restricted cash	144	133	135	182
Southern Power | Other current assets
Restricted cash:
Restricted cash	17	0
Southern Power | Other deferred charges and assets
Restricted cash:
Restricted cash	3	3
Southern Power | Estimated Construction Completion Costs | Deuel Harvest
Restricted cash:
Restricted cash	3	3
Southern Power | Proceeds From Issuance Of Solid Waste Disposal Facility Revenue Bonds
Restricted cash:
Restricted cash	17
Southern Company Gas
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	33	81
Restricted cash:
Total cash, cash equivalents, and restricted cash	35	83	$ 48	$ 19
Southern Company Gas | Other current assets
Restricted cash:
Restricted cash	2	2
Southern Company Gas | Other deferred charges and assets
Restricted cash:
Restricted cash	$ 0	$ 0