Introduction - Schedule of Other Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Subject to amortization:
Gross Carrying Amount	$ 669	$ 669
Accumulated Amortization	(450)	(444)
Other Intangible Assets, Net	219	225
Not subject to amortization:
FCC licenses	75	75
Total other intangible assets
Gross Carrying Amount	744	744
Accumulated Amortization	(450)	(444)
Other Intangible Assets, Net	294	300
Customer relationships
Subject to amortization:
Gross Carrying Amount	212	212
Accumulated Amortization	(190)	(189)
Other Intangible Assets, Net	22	23
Total other intangible assets
Accumulated Amortization	(190)	(189)
Trade names
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
Subject to amortization:
Gross Carrying Amount	390	390
Accumulated Amortization	(193)	(188)
Other Intangible Assets, Net	197	202
Total other intangible assets
Accumulated Amortization	(193)	(188)
Other
Subject to amortization:
Gross Carrying Amount	3	3
Accumulated Amortization	(3)	(3)
Other Intangible Assets, Net	0	0
Total other intangible assets
Accumulated Amortization	(3)	(3)
SOUTHERN POWER CO
Subject to amortization:
Accumulated Amortization	(193)	(188)
Total other intangible assets
Accumulated Amortization	(193)	(188)
SOUTHERN POWER CO | PPA fair value adjustments
Subject to amortization:
Gross Carrying Amount	390	390
Accumulated Amortization	(193)	(188)
Other Intangible Assets, Net	197	202
Total other intangible assets
Accumulated Amortization	(193)	(188)
SOUTHERN Co GAS
Subject to amortization:
Gross Carrying Amount	182	182
Accumulated Amortization	(180)	(179)
Other Intangible Assets, Net	2	3
Total other intangible assets
Accumulated Amortization	(180)	(179)
Other Intangible Assets, Net	2	3
SOUTHERN Co GAS | Customer relationships
Subject to amortization:
Gross Carrying Amount	156	156
Accumulated Amortization	(154)	(153)
Other Intangible Assets, Net	2	3
Total other intangible assets
Accumulated Amortization	(154)	(153)
SOUTHERN Co GAS | Trade names
Subject to amortization:
Gross Carrying Amount	26	26
Accumulated Amortization	(26)	(26)
Other Intangible Assets, Net	0	0
Total other intangible assets
Accumulated Amortization	$ (26)	$ (26)