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FINANCING - Secured Debt (Details) - USD ($)
$ in Millions
Dec. 31, 2019
Oct. 24, 2019
Dec. 31, 2018
Debt Disclosure [Line Items]      
Finance lease obligations $ 226    
Finance lease obligations     $ 197
Georgia Power      
Debt Disclosure [Line Items]      
Finance lease obligations $ 156    
Finance lease obligations     142
Georgia Power | Plant Vogtle Units 3 And 4      
Debt Disclosure [Line Items]      
Percent ownership 45.70%    
Georgia Power | Secured Debt      
Debt Disclosure [Line Items]      
Long-term debt $ 3,999   2,767
Mississippi Power      
Debt Disclosure [Line Items]      
Percent ownership   50.00%  
Finance lease obligations 0    
Mississippi Power | Secured Debt      
Debt Disclosure [Line Items]      
Long-term debt 270   270
Southern Company Gas      
Debt Disclosure [Line Items]      
Finance lease obligations 0    
Southern Company Gas | Secured Debt      
Debt Disclosure [Line Items]      
Long-term debt $ 1,575   $ 1,325