Introduction - Other Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Other intangible assets subject to amortization:
Gross Carrying Amount	$ 740	$ 773
Accumulated Amortization	(265)	(235)
Other Intangible Assets, Net	475	538
Other intangible assets not subject to amortization:
Federal Communications Commission licenses	75	75
Total other intangible assets
Gross Carrying Amount	815	848
Other Intangible Assets, Net	550	613
Customer relationships
Other intangible assets subject to amortization:
Gross Carrying Amount	211	223
Accumulated Amortization	(110)	(94)
Other Intangible Assets, Net	101	129
Trade names
Other intangible assets subject to amortization:
Gross Carrying Amount	64	70
Accumulated Amortization	(23)	(21)
Other Intangible Assets, Net	41	49
Other
Other intangible assets subject to amortization:
Gross Carrying Amount	12	11
Accumulated Amortization	(8)	(5)
Other Intangible Assets, Net	4	6
SOUTHERN POWER CO
Other intangible assets subject to amortization:
Accumulated Amortization	(64)	(61)
SOUTHERN POWER CO | PPA fair value adjustments
Other intangible assets subject to amortization:
Gross Carrying Amount	389	405
Accumulated Amortization	(64)	(61)
Other Intangible Assets, Net	325	344
SOUTHERN Co GAS
Other intangible assets subject to amortization:
Gross Carrying Amount	246	246
Accumulated Amortization	(168)	(145)
Other Intangible Assets, Net	78	101
Total other intangible assets
Other Intangible Assets, Net	78	101
SOUTHERN Co GAS | Customer relationships
Other intangible assets subject to amortization:
Gross Carrying Amount	156	156
Accumulated Amortization	(99)	(84)
Other Intangible Assets, Net	57	72
SOUTHERN Co GAS | Trade names
Other intangible assets subject to amortization:
Gross Carrying Amount	26	26
Accumulated Amortization	(9)	(7)
Other Intangible Assets, Net	17	19
SOUTHERN Co GAS | Storage and transportation contracts
Other intangible assets subject to amortization:
Gross Carrying Amount	64	64
Accumulated Amortization	(60)	(54)
Other Intangible Assets, Net	$ 4	$ 10