v3.10.0.1
Summary of Significant Accounting Policies - Schedule of Specific Impacts of Applying ASC 606 to Revenues from Contracts with Customers (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended 12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Jun. 30, 2016
Dec. 31, 2015
Statements of Income                            
Revenues                   $ 23,495 $ 23,031 $ 19,896    
Other operations and maintenance                   5,889 5,739 5,382    
Taxes other than income taxes                   1,315 1,250 1,113    
Operating Income $ 578 $ 2,174 $ 63 $ 1,376 $ 739 $ 1,991 $ (1,649) $ 1,252   4,191 2,333 4,486    
Other income (expense), net                   114 163 50    
Earnings Before Income Taxes                   2,749 1,068 3,480    
Income taxes                   449 142 951    
Net Income                   2,300 926 2,529    
Net Income (Loss) 269 1,222 (127) 936 500 1,109 (1,348) 665   2,226 842 2,448    
Changes in certain current assets and liabilities —                            
Receivables                   (426) (202) (544)    
Other current assets                   (127) (143) (206)    
Accrued taxes                   267 (142) 1,456    
Other current liabilities                   63 (45) 250    
Balance Sheets                            
Unbilled revenues 654       810         654 810      
Other accounts and notes receivable 813       698         813 698      
Other current assets 162       62         162 62      
Accrued taxes 656       636         656 636      
Other current liabilities 852       874         852 874      
Total Stockholders' Equity 29,039       25,528       $ 26,612 29,039 25,528 26,612   $ 21,982
Natural gas revenues                            
Statements of Income                            
Revenues                   3,854 3,791 1,596    
Other revenues                            
Statements of Income                            
Revenues                   1,239 803 442    
Alabama Power                            
Statements of Income                            
Revenues                   6,032 6,039 5,889    
Other operations and maintenance                   1,669 1,709 1,557    
Taxes other than income taxes                   389 384 380    
Operating Income 164 561 380 372 255 601 440 361   1,477 1,657 1,618    
Other income (expense), net                   20 43 26    
Earnings Before Income Taxes                   1,236 1,434 1,370    
Income taxes                   291 568 531    
Net Income                   945 866 839    
Net Income (Loss) 73 373 259 225 119 325 230 174   930 848 822    
Changes in certain current assets and liabilities —                            
Receivables                   (149) (168) 94    
Other current assets                   30 20 38    
Accrued taxes                   10 (84) 93    
Other current liabilities                   128 3 11    
Balance Sheets                            
Unbilled revenues 150       162         150 162      
Other accounts and notes receivable 51       55         51 55      
Other current assets 18       5         18 5      
Accrued taxes 44       54         44 54      
Other current liabilities 161       53         161 53      
Total Stockholders' Equity 7,477       6,829       6,323 7,477 6,829 6,323   5,992
Alabama Power | Other revenues                            
Statements of Income                            
Revenues                   267 208 215    
Georgia Power                            
Statements of Income                            
Revenues                   8,420 8,310 8,383    
Other operations and maintenance                   1,860 1,724 2,003    
Taxes other than income taxes                   437 409 405    
Operating Income 257 991 (472) 513 452 1,017 621 483   1,289 2,573 2,434    
Other income (expense), net                   115 104 81    
Earnings Before Income Taxes                   1,007 2,258 2,127    
Income taxes                   214 830 780    
Net Income                   793 1,428 1,347    
Net Income (Loss) 173 664 (396) 352 227 580 347 260   793 1,414 1,330    
Changes in certain current assets and liabilities —                            
Receivables                   8 (256) 60    
Other current assets                   (43) (28) (38)    
Accrued taxes                   58 1 131    
Other current liabilities                   (107) (33) 28    
Balance Sheets                            
Unbilled revenues 208       255         208 255      
Other accounts and notes receivable 80       76         80 76      
Other current assets 70       14         70 14      
Other current liabilities 183       198         183 198      
Total Stockholders' Equity 14,323       11,931       11,356 14,323 11,931 11,356   $ 10,719
Georgia Power | Other revenues                            
Statements of Income                            
Revenues                   481 383 394    
Southern Company Gas                            
Statements of Income                            
Revenues                 1,652 3,909 3,920      
Other operations and maintenance                 480 981 945      
Taxes other than income taxes                 71 211 184      
Operating Income 104 374 49 388 109 67 95 389 199 915 660      
Other income (expense), net                 12 1 44      
Earnings Before Income Taxes                 190 836 610      
Income taxes                 76 464 367      
Net Income                 114 372 243      
Net Income (Loss) 78 $ 46 $ (31) $ 279 (60) $ 15 $ 49 $ 239 114 372 243      
Changes in certain current assets and liabilities —                            
Receivables                 (490) (218) (94)      
Other current assets                 (31) 4 (24)      
Accrued taxes                 8 10 110      
Other current liabilities                 24 (22) (8)      
Balance Sheets                            
Unbilled revenues 213       285         213 285      
Other accounts and notes receivable 142       91         142 91      
Other current assets 50       52         50 52      
Accrued taxes 66       40         66 40      
Other current liabilities 130       159         130 159      
Total Stockholders' Equity 8,570       $ 9,022       9,109 8,570 9,022 $ 9,109 $ 8,001  
Southern Company Gas | Natural gas revenues                            
Statements of Income                            
Revenues                 1,591 3,874 3,787      
Southern Company Gas | Other revenues                            
Statements of Income                            
Revenues                 $ 56 55 $ 129      
Balances Without Adoption of ASC 606                            
Statements of Income                            
Other operations and maintenance                   5,830        
Operating Income                   4,243        
Other income (expense), net                   60        
Earnings Before Income Taxes                   2,747        
Income taxes                   448        
Net Income                   2,299        
Net Income (Loss)                   2,225        
Changes in certain current assets and liabilities —                            
Receivables                   (472)        
Other current assets                   (81)        
Accrued taxes                   268        
Other current liabilities                   61        
Balance Sheets                            
Unbilled revenues 728                 728        
Other accounts and notes receivable 814                 814        
Other current assets 87                 87        
Accrued taxes 655                 655        
Other current liabilities 854                 854        
Total Stockholders' Equity 29,038                 29,038        
Balances Without Adoption of ASC 606 | Natural gas revenues                            
Statements of Income                            
Revenues                   3,852        
Balances Without Adoption of ASC 606 | Other revenues                            
Statements of Income                            
Revenues                   1,234        
Balances Without Adoption of ASC 606 | Alabama Power                            
Statements of Income                            
Other operations and maintenance                   1,625        
Taxes other than income taxes                   388        
Operating Income                   1,485        
Other income (expense), net                   12        
Balances Without Adoption of ASC 606 | Alabama Power | Other revenues                            
Statements of Income                            
Revenues                   230        
Balances Without Adoption of ASC 606 | Georgia Power                            
Statements of Income                            
Other operations and maintenance                   1,772        
Operating Income                   1,283        
Other income (expense), net                   121        
Changes in certain current assets and liabilities —                            
Receivables                   1        
Other current assets                   (36)        
Balance Sheets                            
Unbilled revenues 243                 243        
Other accounts and notes receivable 81                 81        
Other current assets 34                 34        
Balances Without Adoption of ASC 606 | Georgia Power | Other revenues                            
Statements of Income                            
Revenues                   387        
Balances Without Adoption of ASC 606 | Southern Company Gas                            
Statements of Income                            
Operating Income                   913        
Earnings Before Income Taxes                   834        
Income taxes                   463        
Net Income                   371        
Net Income (Loss)                   371        
Changes in certain current assets and liabilities —                            
Accrued taxes                   11        
Other current liabilities                   (24)        
Balance Sheets                            
Accrued taxes 65                 65        
Other current liabilities 132                 132        
Total Stockholders' Equity 8,569                 8,569        
Balances Without Adoption of ASC 606 | Southern Company Gas | Natural gas revenues                            
Statements of Income                            
Revenues                   3,872        
Effect of Change                            
Statements of Income                            
Other operations and maintenance                   59        
Operating Income                   (52)        
Other income (expense), net                   54        
Earnings Before Income Taxes                   2        
Income taxes                   1        
Net Income                   1        
Net Income (Loss)                   1        
Changes in certain current assets and liabilities —                            
Receivables                   46        
Other current assets                   (46)        
Accrued taxes                   (1)        
Other current liabilities                   2        
Balance Sheets                            
Unbilled revenues (74)                 (74)        
Other accounts and notes receivable (1)                 (1)        
Other current assets 75                 75        
Accrued taxes 1                 1        
Other current liabilities (2)                 (2)        
Total Stockholders' Equity 1                 1        
Effect of Change | Natural gas revenues                            
Statements of Income                            
Revenues                   2        
Effect of Change | Other revenues                            
Statements of Income                            
Revenues                   5        
Effect of Change | Alabama Power                            
Statements of Income                            
Other operations and maintenance                   44        
Taxes other than income taxes                   1        
Operating Income                   (8)        
Other income (expense), net                   8        
Effect of Change | Alabama Power | Other revenues                            
Statements of Income                            
Revenues                   37        
Effect of Change | Georgia Power                            
Statements of Income                            
Other operations and maintenance                   88        
Operating Income                   6        
Other income (expense), net                   (6)        
Changes in certain current assets and liabilities —                            
Receivables                   7        
Other current assets                   (7)        
Balance Sheets                            
Unbilled revenues (35)                 (35)        
Other accounts and notes receivable (1)                 (1)        
Other current assets 36                 36        
Effect of Change | Georgia Power | Other revenues                            
Statements of Income                            
Revenues                   94        
Effect of Change | Southern Company Gas                            
Statements of Income                            
Operating Income                   2        
Earnings Before Income Taxes                   2        
Income taxes                   1        
Net Income                   1        
Net Income (Loss)                   1        
Changes in certain current assets and liabilities —                            
Accrued taxes                   (1)        
Other current liabilities                   2        
Balance Sheets                            
Accrued taxes 1                 1        
Other current liabilities (2)                 (2)        
Total Stockholders' Equity $ 1                 1        
Effect of Change | Southern Company Gas | Natural gas revenues                            
Statements of Income                            
Revenues                   $ 2