SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of AOCI (Loss) Balances, Net of Tax Effects (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 34,532	$ 32,276	$ 32,234
Total other comprehensive income	(10)	71	158
Ending balance	35,225	34,532	32,276
Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(149)
Total other comprehensive income	28
Ending balance	(121)	(149)
Pension and Other Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(18)
Total other comprehensive income	(38)
Ending balance	(56)	(18)
Accumulated Other Comprehensive Income (Loss)(*)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(167)	(237)	(395)
Total other comprehensive income	(10)
Ending balance	(177)	(167)	(237)
Southern Power
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	6,916	6,598	6,631
Total other comprehensive income	1	10	40
Ending balance	6,698	6,916	6,598
Southern Power | Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(9)
Total other comprehensive income	8
Ending balance	(1)	(9)
Southern Power | Pension and Other Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(9)
Total other comprehensive income	(7)
Ending balance	(16)	(9)
Southern Power | Accumulated Other Comprehensive Income (Loss)(*)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(18)	(27)	(67)
Total other comprehensive income	1
Ending balance	(17)	(18)	(27)
Southern Company Gas
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total other comprehensive income	(15)	7	$ 46
Southern Company Gas | Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(25)
Total other comprehensive income	1
Ending balance	(24)	(25)
Southern Company Gas | Pension and Other Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	56
Total other comprehensive income	(16)
Ending balance	40	56
Southern Company Gas | Accumulated Other Comprehensive Income (Loss)(*)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	31
Total other comprehensive income	(15)
Ending balance	$ 16	$ 31