SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Other Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 677	$ 740
Accumulated Amortization	(307)	(328)
Other Intangible Assets, Net	370	412
Intangible assets, gross	752	815
Intangible assets, net	445	487
Federal Communications Commission licenses
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	75	75
Accumulated Amortization	0	0
Other Intangible Assets, Net	75	75
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	212	212
Accumulated Amortization	(150)	(135)
Other Intangible Assets, Net	62	77
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	64	64
Accumulated Amortization	(38)	(31)
Other Intangible Assets, Net	26	33
Storage and transportation contracts
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	0	64
Accumulated Amortization	0	(64)
Other Intangible Assets, Net	0	0
PPA fair value adjustments
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	390	390
Accumulated Amortization	(109)	(89)
Other Intangible Assets, Net	281	301
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	11	10
Accumulated Amortization	(10)	(9)
Other Intangible Assets, Net	1	1
Southern Power
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	(109)	(89)
Southern Power | PPA fair value adjustments
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	390	390
Accumulated Amortization	(109)	(89)
Other Intangible Assets, Net	281	301
Southern Company Gas
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	182	246
Accumulated Amortization	(145)	(195)
Other Intangible Assets, Net	37	51
Intangible assets, net	37	51
Southern Company Gas | Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	156	156
Accumulated Amortization	(130)	(119)
Other Intangible Assets, Net	26	37
Southern Company Gas | Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	26	26
Accumulated Amortization	(15)	(12)
Other Intangible Assets, Net	11	14
Southern Company Gas | Storage and transportation contracts
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	0	64
Accumulated Amortization	0	(64)
Other Intangible Assets, Net	$ 0	$ 0