PROPERTY, PLANT, AND EQUIPMENT - Depreciation and Amortization (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 37,725	$ 35,297
Utility plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	36,600	34,300
Other plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 1,100	1,000
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	$ 5,534	5,276
Southern Company Gas | Utility plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	5,300	5,100
Southern Company Gas | Other plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 210	$ 184
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