Property, Plant, and Equipment - Depreciation and Amortization (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended		36 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 31,038	$ 31,457
Other plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 766	673
Other plant in service | Maximum
Property, Plant and Equipment [Line Items]
Depreciation of original cost	65 years
Utility plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 30,300	30,800
Georgia Power
Property, Plant and Equipment [Line Items]
Amortization of remaining regulatory liability			$ 14
Accumulated depreciation	12,096	11,704
Gulf Power
Property, Plant and Equipment [Line Items]
Decrease in depreciation		34
Southern Company Gas
Property, Plant and Equipment [Line Items]
Accumulated depreciation	4,400	4,596
Southern Company Gas | Other plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 129	75
Southern Company Gas | Transportation equipment | Minimum
Property, Plant and Equipment [Line Items]
Depreciation of original cost	5 years
Southern Company Gas | Transportation equipment | Maximum
Property, Plant and Equipment [Line Items]
Depreciation of original cost	15 years
Southern Company Gas | Storage facilities | Minimum
Property, Plant and Equipment [Line Items]
Depreciation of original cost	40 years
Southern Company Gas | Storage facilities | Maximum
Property, Plant and Equipment [Line Items]
Depreciation of original cost	60 years
Southern Company Gas | Other assets | Maximum
Property, Plant and Equipment [Line Items]
Depreciation of original cost	65 years
Southern Company Gas | Utility plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 4,300	$ 4,500