Introduction - Other Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Other intangible assets subject to amortization:
Gross Carrying Amount	$ 761	$ 773
Accumulated Amortization	(251)	(235)
Other Intangible Assets, Net	510	538
Other intangible assets not subject to amortization:
Federal Communications Commission licenses	75	75
Total other intangible assets
Gross Carrying Amount	836	848
Other Intangible Assets, Net	585	613
Customer relationships
Other intangible assets subject to amortization:
Gross Carrying Amount	211	223
Accumulated Amortization	(100)	(94)
Other Intangible Assets, Net	111	129
Trade names
Other intangible assets subject to amortization:
Gross Carrying Amount	70	70
Accumulated Amortization	(22)	(21)
Other Intangible Assets, Net	48	49
Other
Other intangible assets subject to amortization:
Gross Carrying Amount	11	11
Accumulated Amortization	(6)	(5)
Other Intangible Assets, Net	5	6
SOUTHERN POWER CO
Other intangible assets subject to amortization:
Accumulated Amortization	(67)	(61)
SOUTHERN POWER CO | PPA fair value adjustments
Other intangible assets subject to amortization:
Gross Carrying Amount	405	405
Accumulated Amortization	(67)	(61)
Other Intangible Assets, Net	338	344
SOUTHERN Co GAS
Other intangible assets subject to amortization:
Gross Carrying Amount	246	246
Accumulated Amortization	(153)	(145)
Other Intangible Assets, Net	93	101
Total other intangible assets
Other Intangible Assets, Net	93	101
SOUTHERN Co GAS | Customer relationships
Other intangible assets subject to amortization:
Gross Carrying Amount	156	156
Accumulated Amortization	(89)	(84)
Other Intangible Assets, Net	67	72
SOUTHERN Co GAS | Trade names
Other intangible assets subject to amortization:
Gross Carrying Amount	26	26
Accumulated Amortization	(8)	(7)
Other Intangible Assets, Net	18	19
SOUTHERN Co GAS | Storage and transportation contracts
Other intangible assets subject to amortization:
Gross Carrying Amount	64	64
Accumulated Amortization	(56)	(54)
Other Intangible Assets, Net	$ 8	$ 10