Introduction - Schedule of Other Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Subject to amortization:
Gross Carrying Amount	$ 669	$ 669
Accumulated Amortization	(436)	(412)
Other Intangible Assets, Net	233	257
Not subject to amortization:
FCC licenses	75	75
Total other intangible assets
Gross Carrying Amount	744	744
Accumulated Amortization	(436)	(412)
Other Intangible Assets, Net	308	332
Customer relationships
Subject to amortization:
Gross Carrying Amount	212	212
Accumulated Amortization	(186)	(182)
Other Intangible Assets, Net	26	30
Total other intangible assets
Accumulated Amortization	(186)	(182)
Trade names
Subject to amortization:
Gross Carrying Amount	64	64
Accumulated Amortization	(64)	(59)
Other Intangible Assets, Net	0	5
Total other intangible assets
Accumulated Amortization	(64)	(59)
PPA fair value adjustments
Subject to amortization:
Gross Carrying Amount	390	390
Accumulated Amortization	(183)	(168)
Other Intangible Assets, Net	207	222
Total other intangible assets
Accumulated Amortization	(183)	(168)
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	(183)	(168)
Total other intangible assets
Accumulated Amortization	(183)	(168)
SOUTHERN POWER CO | PPA fair value adjustments
Subject to amortization:
Gross Carrying Amount	390	390
Accumulated Amortization	(183)	(168)
Other Intangible Assets, Net	207	222
Total other intangible assets
Accumulated Amortization	(183)	(168)
SOUTHERN Co GAS
Subject to amortization:
Gross Carrying Amount	182	182
Accumulated Amortization	(178)	(173)
Other Intangible Assets, Net	4	9
Total other intangible assets
Accumulated Amortization	(178)	(173)
Other Intangible Assets, Net	4	9
SOUTHERN Co GAS | Customer relationships
Subject to amortization:
Gross Carrying Amount	156	156
Accumulated Amortization	(152)	(150)
Other Intangible Assets, Net	4	6
Total other intangible assets
Accumulated Amortization	(152)	(150)
SOUTHERN Co GAS | Trade names
Subject to amortization:
Gross Carrying Amount	26	26
Accumulated Amortization	(26)	(23)
Other Intangible Assets, Net	0	3
Total other intangible assets
Accumulated Amortization	$ (26)	$ (23)