Joint Ownership Agreements (Details) $ in Millions	Dec. 31, 2017 USD ($) MW	Aug. 31, 2016
ALABAMA POWER CO
Jointly owned utility plant interests
Percent ownership	14.00%
Total megawatt capacity | MW	1,000
ALABAMA POWER CO | Plant Miller (coal) Units 1 and 2
Jointly owned utility plant interests
Percent ownership	91.84%
Plant in service	$ 1,717
Accumulated depreciation	619
Construction Work in Progress	$ 54
Total megawatt capacity | MW	1,320
ALABAMA POWER CO | Greene County
Jointly owned utility plant interests
Percent ownership	60.00%
Plant in service	$ 172
Accumulated depreciation	65
Construction Work in Progress	$ 2
Total megawatt capacity | MW	500
ALABAMA POWER CO | SEGCO
Jointly owned utility plant interests
Percent ownership	86.00%
GEORGIA POWER CO | Plant Vogtle (nuclear) Units 1 and 2
Jointly owned utility plant interests
Percent ownership	45.70%
Plant in service	$ 3,564
Accumulated depreciation	2,141
Construction Work in Progress	$ 70
GEORGIA POWER CO | Plant Hatch (nuclear)
Jointly owned utility plant interests
Percent ownership	50.10%
Plant in service	$ 1,321
Accumulated depreciation	595
Construction Work in Progress	$ 87
GEORGIA POWER CO | Plant Scherer (coal) Units 1 and 2
Jointly owned utility plant interests
Percent ownership	8.40%
Plant in service	$ 261
Accumulated depreciation	93
Construction Work in Progress	$ 8
GEORGIA POWER CO | Plant Wansley (coal)
Jointly owned utility plant interests
Percent ownership	53.50%
Plant in service	$ 1,053
Accumulated depreciation	335
Construction Work in Progress	$ 72
GEORGIA POWER CO | Rocky Mountain (pumped storage)
Jointly owned utility plant interests
Percent ownership	25.40%
Plant in service	$ 182
Accumulated depreciation	132
Construction Work in Progress	$ 0
GEORGIA POWER CO | Plant Scherer Unit 3 (coal)
Jointly owned utility plant interests
Percent ownership	75.00%
Plant in service	$ 1,232
Accumulated depreciation	468
Construction Work in Progress	$ 26
GEORGIA POWER CO | Intercession City Combustion Turbine
Jointly owned utility plant interests
Percent ownership		33.00%
GULF POWER CO | Plant Scherer Unit 3 (coal)
Jointly owned utility plant interests
Percent ownership	25.00%
Plant in service	$ 374
Accumulated depreciation	147
Construction Work in Progress	$ 9
Total megawatt capacity | MW	818
GULF POWER CO | Plant Daniel Units 1 & 2 (coal)
Jointly owned utility plant interests
Percent ownership	50.00%
Plant in service	$ 696
Accumulated depreciation	225
Construction Work in Progress	$ 4
Total megawatt capacity | MW	1,000
MISSISSIPPI POWER CO | Plant Daniel Units 1 & 2 (coal)
Jointly owned utility plant interests
Percent ownership	50.00%
SOUTHERN POWER CO
Jointly owned utility plant interests
Total megawatt capacity | MW	659
SOUTHERN POWER CO | Plant Stanton (combined cycle) Unit A
Jointly owned utility plant interests
Percent ownership	65.00%
Plant in service	$ 155
Accumulated depreciation	55
Construction Work in Progress	$ 0
SOUTHERN POWER CO | Dalton Pipeline (natural gas pipeline)
Jointly owned utility plant interests
Percent ownership	50.00%
Plant in service	$ 241
Accumulated depreciation	2
Construction Work in Progress	$ 13
GULF POWER CO | MISSISSIPPI POWER CO | Plant Daniel Units 1 & 2 (coal)
Jointly owned utility plant interests
Percent ownership	50.00%
Plant in service	$ 713
Accumulated depreciation	189
Construction Work in Progress	$ 4
Total megawatt capacity | MW	1,000
ALABAMA POWER CO | MISSISSIPPI POWER CO | Greene County
Jointly owned utility plant interests
Percent ownership	40.00%
Plant in service	$ 164
Accumulated depreciation	55
Construction Work in Progress	$ 1
Total megawatt capacity | MW	500