v3.10.0.1
Revenue from Contracts with Customers - Disaggregate Revenue Sources (Details) - USD ($)
$ in Millions
 6 Months Ended 12 Months Ended
Dec. 31, 2016
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disaggregation of Revenue [Line Items]        
Total operating revenues   $ 23,495 $ 23,031 $ 19,896
Other income   322    
Retail electric revenues        
Disaggregation of Revenue [Line Items]        
Leases revenues   75    
Increase (decrease) in revenue from cost recovery mechanisms   60    
Residential        
Disaggregation of Revenue [Line Items]        
Total operating revenues   6,608    
Commercial        
Disaggregation of Revenue [Line Items]        
Total operating revenues   5,266    
Industrial        
Disaggregation of Revenue [Line Items]        
Total operating revenues   3,224    
Other        
Disaggregation of Revenue [Line Items]        
Total operating revenues   124    
Natural gas distribution revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   3,175    
Alternative revenue programs        
Disaggregation of Revenue [Line Items]        
Total operating revenues   (20)    
Total retail electric and gas distribution revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   18,377    
Wholesale energy revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   1,896    
Revenue from transactions accounted for as derivatives   299    
Lease income from PPA contracts   384    
Wholesale capacity revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   620    
Lease income from PPA contracts   121    
Other natural gas revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   699    
Other revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   1,903    
Southern Company Gas        
Disaggregation of Revenue [Line Items]        
Total operating revenues $ 1,652 3,909 3,920  
Southern Company Gas | Natural gas distribution revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   3,155    
Southern Company Gas | Residential        
Disaggregation of Revenue [Line Items]        
Total operating revenues   1,525    
Southern Company Gas | Commercial        
Disaggregation of Revenue [Line Items]        
Total operating revenues   436    
Southern Company Gas | Transportation        
Disaggregation of Revenue [Line Items]        
Total operating revenues   944    
Southern Company Gas | Industrial        
Disaggregation of Revenue [Line Items]        
Total operating revenues   40    
Southern Company Gas | Other        
Disaggregation of Revenue [Line Items]        
Total operating revenues   230    
Southern Company Gas | Alternative revenue programs        
Disaggregation of Revenue [Line Items]        
Total operating revenues   (20)    
Southern Company Gas | Gas marketing services        
Disaggregation of Revenue [Line Items]        
Total operating revenues   568    
Other income   3    
Southern Company Gas | Wholesale gas services        
Disaggregation of Revenue [Line Items]        
Total operating revenues   101    
Southern Company Gas | Gas midstream operations        
Disaggregation of Revenue [Line Items]        
Total operating revenues   32    
Southern Company Gas | Other revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   53    
Alabama Power        
Disaggregation of Revenue [Line Items]        
Total operating revenues   6,032 6,039 5,889
Other income   57    
Alabama Power | Retail electric revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   5,367    
Increase (decrease) in revenue from cost recovery mechanisms   152    
Alabama Power | Residential        
Disaggregation of Revenue [Line Items]        
Total operating revenues   2,335    
Alabama Power | Commercial        
Disaggregation of Revenue [Line Items]        
Total operating revenues   1,578    
Alabama Power | Industrial        
Disaggregation of Revenue [Line Items]        
Total operating revenues   1,428    
Alabama Power | Other        
Disaggregation of Revenue [Line Items]        
Total operating revenues   26    
Alabama Power | Wholesale energy revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   297    
Revenue from transactions accounted for as derivatives   20    
Alabama Power | Wholesale capacity revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   101    
Alabama Power | Other revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   267    
Georgia Power        
Disaggregation of Revenue [Line Items]        
Total operating revenues   8,420 8,310 8,383
Other income   109    
Georgia Power | Retail electric revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   7,752    
Leases revenues   74    
Increase (decrease) in revenue from cost recovery mechanisms   (19)    
Georgia Power | Residential        
Disaggregation of Revenue [Line Items]        
Total operating revenues   3,301    
Georgia Power | Commercial        
Disaggregation of Revenue [Line Items]        
Total operating revenues   3,023    
Georgia Power | Industrial        
Disaggregation of Revenue [Line Items]        
Total operating revenues   1,344    
Georgia Power | Other        
Disaggregation of Revenue [Line Items]        
Total operating revenues   84    
Georgia Power | Wholesale energy revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   133    
Revenue from transactions accounted for as derivatives   29    
Georgia Power | Wholesale capacity revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   54    
Georgia Power | Other revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   481    
Leases revenues   135    
Mississippi Power        
Disaggregation of Revenue [Line Items]        
Total operating revenues   1,265 1,187 1,163
Mississippi Power | Retail electric revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   889    
Increase (decrease) in revenue from cost recovery mechanisms   (13)    
Mississippi Power | Residential        
Disaggregation of Revenue [Line Items]        
Total operating revenues   273    
Mississippi Power | Commercial        
Disaggregation of Revenue [Line Items]        
Total operating revenues   286    
Mississippi Power | Industrial        
Disaggregation of Revenue [Line Items]        
Total operating revenues   321    
Mississippi Power | Other        
Disaggregation of Revenue [Line Items]        
Total operating revenues   9    
Mississippi Power | Wholesale energy revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   348    
Revenue from transactions accounted for as derivatives   4    
Mississippi Power | Wholesale capacity revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   6    
Mississippi Power | Other revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   22    
Southern Power        
Disaggregation of Revenue [Line Items]        
Total operating revenues   2,205 2,075 $ 1,577
Southern Power | PPA capacity revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   580    
Lease income from PPA contracts   186    
Southern Power | PPA energy revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   1,140    
Revenue from transactions accounted for as derivatives   242    
Lease income from PPA contracts   413    
Southern Power | Non-PPA revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   472    
Southern Power | Other revenues        
Disaggregation of Revenue [Line Items]        
Total operating revenues   13    
Operating Segments | Southern Company Gas        
Disaggregation of Revenue [Line Items]        
Total operating revenues 1,723 3,930 4,090  
Wholesale gas services | Operating Segments | Southern Company Gas        
Disaggregation of Revenue [Line Items]        
Total operating revenues 24 144 6  
Wholesale gas services | Third Party Gross Revenues | Operating Segments | Southern Company Gas        
Disaggregation of Revenue [Line Items]        
Total operating revenues $ 5,807 6,955 $ 6,152  
Revenue from transactions accounted for as derivatives   $ 3,900