PROPERTY, PLANT, AND EQUIPMENT - Deferred Cloud Implementation Costs (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	$ 17,259	$ 16,298
Deferred Cloud Implementation Costs
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	240	162
Alabama Power
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	4,549	4,262
Alabama Power | Deferred Cloud Implementation Costs
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	54	38
Georgia Power
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	8,823	8,297
Georgia Power | Deferred Cloud Implementation Costs
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	81	58
Mississippi Power
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	877	805
Mississippi Power | Deferred Cloud Implementation Costs
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	11	7
Southern Power
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	967	1,150
Southern Power | Deferred Cloud Implementation Costs
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	14	9
Southern Company Gas
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	1,064	931
Southern Company Gas | Deferred Cloud Implementation Costs
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	$ 35	$ 17