Introduction - Schedule of Other Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Other intangible assets subject to amortization:
Gross Carrying Amount	$ 676	$ 740
Accumulated Amortization	(296)	(328)
Other Intangible Assets, Net	380	412
Other intangible assets not subject to amortization:
Federal Communications Commission licenses	75	75
Total other intangible assets
Gross Carrying Amount	751	815
Accumulated Amortization	(296)	(328)
Other Intangible Assets, Net	455	487
Customer relationships
Other intangible assets subject to amortization:
Gross Carrying Amount	212	212
Accumulated Amortization	(148)	(135)
Other Intangible Assets, Net	64	77
Total other intangible assets
Accumulated Amortization	(148)	(135)
Trade names
Other intangible assets subject to amortization:
Gross Carrying Amount	64	64
Accumulated Amortization	(36)	(31)
Other Intangible Assets, Net	28	33
Total other intangible assets
Accumulated Amortization	(36)	(31)
Storage and transportation contracts
Other intangible assets subject to amortization:
Gross Carrying Amount	0	64
Accumulated Amortization	0	(64)
Other Intangible Assets, Net	0	0
Total other intangible assets
Accumulated Amortization	0	(64)
PPA fair value adjustments
Other intangible assets subject to amortization:
Gross Carrying Amount	390	390
Accumulated Amortization	(104)	(89)
Other Intangible Assets, Net	286	301
Total other intangible assets
Accumulated Amortization	(104)	(89)
Other
Other intangible assets subject to amortization:
Gross Carrying Amount	10	10
Accumulated Amortization	(8)	(9)
Other Intangible Assets, Net	2	1
Total other intangible assets
Accumulated Amortization	(8)	(9)
SOUTHERN POWER CO
Other intangible assets subject to amortization:
Accumulated Amortization	(104)	(89)
Total other intangible assets
Accumulated Amortization	(104)	(89)
SOUTHERN POWER CO | PPA fair value adjustments
Other intangible assets subject to amortization:
Gross Carrying Amount	390	390
Accumulated Amortization	(104)	(89)
Other Intangible Assets, Net	286	301
Total other intangible assets
Accumulated Amortization	(104)	(89)
SOUTHERN Co GAS
Other intangible assets subject to amortization:
Gross Carrying Amount	182	246
Accumulated Amortization	(142)	(195)
Other Intangible Assets, Net	40	51
Total other intangible assets
Accumulated Amortization	(142)	(195)
Other Intangible Assets, Net	40	51
SOUTHERN Co GAS | Customer relationships
Other intangible assets subject to amortization:
Gross Carrying Amount	156	156
Accumulated Amortization	(128)	(119)
Other Intangible Assets, Net	28	37
Total other intangible assets
Accumulated Amortization	(128)	(119)
SOUTHERN Co GAS | Trade names
Other intangible assets subject to amortization:
Gross Carrying Amount	26	26
Accumulated Amortization	(14)	(12)
Other Intangible Assets, Net	12	14
Total other intangible assets
Accumulated Amortization	(14)	(12)
SOUTHERN Co GAS | Storage and transportation contracts
Other intangible assets subject to amortization:
Gross Carrying Amount	0	64
Accumulated Amortization	0	(64)
Other Intangible Assets, Net	0	0
Total other intangible assets
Accumulated Amortization	$ 0	$ (64)