Introduction - Schedule of Other Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Other intangible assets subject to amortization:
Gross Carrying Amount	$ 741	$ 740
Accumulated Amortization	(339)	(328)
Other Intangible Assets, Net	402	412
Other intangible assets not subject to amortization:
Federal Communications Commission licenses	75	75
Total other intangible assets
Gross Carrying Amount	816	815
Accumulated Amortization	(339)	(328)
Other Intangible Assets, Net	477	487
Customer relationships
Other intangible assets subject to amortization:
Gross Carrying Amount	212	212
Accumulated Amortization	(139)	(135)
Other Intangible Assets, Net	73	77
Total other intangible assets
Accumulated Amortization	(139)	(135)
Trade names
Other intangible assets subject to amortization:
Gross Carrying Amount	64	64
Accumulated Amortization	(33)	(31)
Other Intangible Assets, Net	31	33
Total other intangible assets
Accumulated Amortization	(33)	(31)
Storage and transportation contracts
Other intangible assets subject to amortization:
Gross Carrying Amount	64	64
Accumulated Amortization	(64)	(64)
Other Intangible Assets, Net	0	0
Total other intangible assets
Accumulated Amortization	(64)	(64)
PPA fair value adjustments
Other intangible assets subject to amortization:
Gross Carrying Amount	390	390
Accumulated Amortization	(94)	(89)
Other Intangible Assets, Net	296	301
Total other intangible assets
Accumulated Amortization	(94)	(89)
Other
Other intangible assets subject to amortization:
Gross Carrying Amount	11	10
Accumulated Amortization	(9)	(9)
Other Intangible Assets, Net	2	1
Total other intangible assets
Accumulated Amortization	(9)	(9)
SOUTHERN POWER CO
Other intangible assets subject to amortization:
Accumulated Amortization	(94)	(89)
Total other intangible assets
Accumulated Amortization	(94)	(89)
SOUTHERN POWER CO | PPA fair value adjustments
Other intangible assets subject to amortization:
Gross Carrying Amount	390	390
Accumulated Amortization	(94)	(89)
Other Intangible Assets, Net	296	301
Total other intangible assets
Accumulated Amortization	(94)	(89)
SOUTHERN Co GAS
Other intangible assets subject to amortization:
Gross Carrying Amount	246	246
Accumulated Amortization	(199)	(195)
Other Intangible Assets, Net	47	51
Total other intangible assets
Accumulated Amortization	(199)	(195)
Other Intangible Assets, Net	47	51
SOUTHERN Co GAS | Customer relationships
Other intangible assets subject to amortization:
Gross Carrying Amount	156	156
Accumulated Amortization	(122)	(119)
Other Intangible Assets, Net	34	37
Total other intangible assets
Accumulated Amortization	(122)	(119)
SOUTHERN Co GAS | Trade names
Other intangible assets subject to amortization:
Gross Carrying Amount	26	26
Accumulated Amortization	(13)	(12)
Other Intangible Assets, Net	13	14
Total other intangible assets
Accumulated Amortization	(13)	(12)
SOUTHERN Co GAS | Storage and transportation contracts
Other intangible assets subject to amortization:
Gross Carrying Amount	64	64
Accumulated Amortization	(64)	(64)
Other Intangible Assets, Net	0	0
Total other intangible assets
Accumulated Amortization	$ (64)	$ (64)