PROPERTY, PLANT, AND EQUIPMENT - Depreciation and Amortization (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 35,297	$ 34,079
Utility plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	34,300	33,100
Other plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 963	930
Other plant in service | Maximum
Property, Plant and Equipment [Line Items]
Depreciation period of original cost	30 years
Southern Company Gas
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 5,276	5,067
Southern Company Gas | Utility plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	5,100	4,800
Southern Company Gas | Other plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 184	$ 219
Southern Company Gas | Transportation equipment | Minimum
Property, Plant and Equipment [Line Items]
Depreciation period of original cost	5 years
Southern Company Gas | Transportation equipment | Maximum
Property, Plant and Equipment [Line Items]
Depreciation period of original cost	12 years
Southern Company Gas | Storage facilities | Minimum
Property, Plant and Equipment [Line Items]
Depreciation period of original cost	30 years
Southern Company Gas | Storage facilities | Maximum
Property, Plant and Equipment [Line Items]
Depreciation period of original cost	75 years
Southern Company Gas | Other assets | Maximum
Property, Plant and Equipment [Line Items]
Depreciation period of original cost	75 years