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Regulatory Matters - Schedule of SO Regulatory Assets and Liabilities (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 720 $ (1,894)  
Maximum      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Life of new issue 50 years    
Southern Company Gas      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ (1,872) (1,879)  
Alabama Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ (769) (1,088)  
Alabama Power | Maximum      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Life of new issue 50 years    
Mississippi Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ (35) (42)  
Regulatory amortization period 5 years    
Georgia Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 2,378 232  
Customer refund liability, current 55    
Customer refund $ 40    
Georgia Power | Maximum      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Life of new issue 34 years    
Deferred income tax credits      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ (6,455) (7,261)  
Deferred income tax credits | Southern Company Gas      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net (940) (1,063)  
Deferred income tax credits | Alabama Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net (2,027) (2,082)  
Deferred income tax credits | Georgia Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net (3,080) (3,248)  
Other cost of removal obligations      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net (2,297) (2,684)  
Other cost of removal obligations | Southern Company Gas      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net (1,585) (1,646)  
Other cost of removal obligations | Alabama Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net (497) (609)  
Other cost of removal obligations | Mississippi Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net (185) (178)  
Customer refunds      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net (293) (188)  
Customer refunds | Georgia Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net (165) (188)  
Property damage reserves-liability      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net (76) (135)  
Property damage reserves-liability | Mississippi Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net (56) (57)  
Over recovered regulatory clause revenues      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net (47) (155)  
Over recovered regulatory clause revenues | Southern Company Gas      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net (43) (144)  
Other regulatory liabilities      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ (132) (104)  
Other regulatory liabilities | Maximum      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Regulatory liability amortization period 20 years    
Other regulatory liabilities | Southern Company Gas      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ (46) (21)  
Other regulatory liabilities | Alabama Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net (45) (7)  
Other regulatory liabilities | Mississippi Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ (9) 0  
Regulatory amortization period 1 year    
Other regulatory liabilities | Georgia Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ (7) (3)  
Retiree benefit plans      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net 3,658 3,931  
Regulatory asset $ 28    
Retiree benefit plans | Maximum      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Regulatory amortization period 15 years    
Retiree benefit plans | Southern Company Gas      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 161 270  
Retiree benefit plans | Southern Company Gas | Maximum      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Regulatory amortization period 15 years    
Retiree benefit plans | Alabama Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 947 946  
Retiree benefit plans | Alabama Power | Maximum      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Regulatory amortization period 15 years    
Retiree benefit plans | Mississippi Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Regulatory amortization period 15 years    
Retiree benefit plans | Georgia Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 1,295 1,313  
Retiree benefit plans | Georgia Power | Maximum      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Regulatory amortization period 14 years    
Asset retirement obligations-asset      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 2,933 1,133  
Asset retirement obligations-asset | Mississippi Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 143 95  
Regulatory amortization period 48 years    
Asset retirement obligations-asset | Georgia Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 2,644 945  
Deferred income tax charges      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 799 814  
Deferred income tax charges | Maximum      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Regulatory amortization period 80 years    
Deferred income tax charges | Alabama Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 241 240  
Regulatory amortization period 50 years    
Deferred income tax charges | Alabama Power | Maximum      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Regulatory amortization period 50 years    
Deferred income tax charges | Mississippi Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 34 36  
Deferred income tax charges | Georgia Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net 522 521  
Property damage reserves-asset      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net 416 333  
Under recovered regulatory clause revenues      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net 407 317  
Under recovered regulatory clause revenues | Southern Company Gas      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 90 98  
Regulatory amortization period 7 years    
Under recovered regulatory clause revenues | Alabama Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 142 142  
Environmental remediation-asset      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net 366 511  
Loss on reacquired debt      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net 346 223  
Loss on reacquired debt | Alabama Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net 56 62  
Loss on reacquired debt | Mississippi Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net 8    
Loss on reacquired debt | Georgia Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net 277 127  
Remaining net book value of retired assets      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 211 306  
Remaining net book value of retired assets | Maximum      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Regulatory amortization period 8 years    
Remaining net book value of retired assets | Alabama Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Regulatory amortization period 8 years    
Remaining net book value of retired assets | Mississippi Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 41 44  
Remaining net book value of retired assets | Georgia Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 127 146  
Remaining net book value of retired assets | Georgia Power | Maximum      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Regulatory amortization period 3 years    
Vacation pay      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 182 183  
Regulatory amortization period 1 year    
Vacation pay | Alabama Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 71 70  
Regulatory amortization period 1 year    
Vacation pay | Mississippi Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 9    
Vacation pay | Georgia Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 91 91  
Regulatory amortization period 1 year    
Long-term debt fair value adjustment      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 121 138  
Long-term debt fair value adjustment | Southern Company Gas      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 121 138  
Long-term debt fair value adjustment | Southern Company Gas | Maximum      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Regulatory amortization period 20 years    
Deferred PPA charges      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 0 119  
Other regulatory assets      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 581 625  
Other regulatory assets | Maximum      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Regulatory amortization period 50 years    
Other regulatory assets | Southern Company Gas      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 59 79  
Other regulatory assets | Southern Company Gas | Maximum      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Regulatory amortization period 10 years    
Other regulatory assets | Alabama Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 57 58  
Regulatory amortization period 12 months    
Other regulatory assets | Mississippi Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 28 28  
Regulatory amortization period 3 years    
Other regulatory assets | Mississippi Power | Maximum      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Regulatory amortization period 50 years    
Other regulatory assets | Georgia Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 135 106  
Regulatory amortization period 24 months    
Asset Group 1 | Maximum      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Regulatory amortization period 10 years    
Kemper IGCC | Mississippi Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net $ 69 88  
Regulatory asset 91    
Storm damage reserves | Georgia Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Total regulatory assets (liabilities), net 416 333  
Major storms      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Storm damage reserves 74 41 $ 40
Major storms | Alabama Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Storm damage reserves 16 4 3
Major storms | Mississippi Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Storm damage reserves 1 3 4
Major storms | Georgia Power      
Schedule of Regulatory Assets and Liabilities [Line Items]      
Storm damage reserves $ 30 $ 30 $ 30