SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of AOCI (Loss) Balances, Net of Tax Effects (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 32,276	$ 32,234	$ 31,759
Current period change	71	158	(75)
Ending balance	34,532	32,276	32,234
Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(162)
Current period change	13
Ending balance	(149)	(162)
Pension and Other Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(76)
Current period change	58
Ending balance	(18)	(76)
Accumulated Other Comprehensive Income (Loss)(*)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(237)	(395)	(321)
Current period change	71
Ending balance	(167)	(237)	(395)
Southern Power
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	6,598	6,631	6,622
Current period change	10	40	(42)
Ending balance	6,916	6,598	6,631
Southern Power | Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	1
Current period change	(10)
Ending balance	(9)	1
Southern Power | Pension and Other Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(29)
Current period change	20
Ending balance	(9)	(29)
Southern Power | Accumulated Other Comprehensive Income (Loss)(*)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(27)	(67)	(26)
Current period change	10
Ending balance	(18)	(27)	(67)
Southern Company Gas
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	9,916	9,767	9,506
Current period change	7	46	(29)
Ending balance	10,397	9,916	9,767
Southern Company Gas | Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(14)
Current period change	(11)
Ending balance	(25)	(14)
Southern Company Gas | Pension and Other Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	38
Current period change	18
Ending balance	56	38
Southern Company Gas | Accumulated Other Comprehensive Income (Loss)(*)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	24	(22)	7
Current period change	7
Ending balance	$ 31	$ 24	$ (22)