v3.10.0.1
Derivatives - Financial Statement Presentation (Details) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Fair value of energy-related derivatives and interest rate derivatives    
Collateral already posted, aggregate fair value $ 277 $ 193
Weather derivative premium 8 11
Parent Company    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 837 700
Derivative asset, gross amount offset (524) (405)
Derivative asset, net amounts recognized in the balance sheets 313 295
Derivative liability, gross amounts recognized 1,036 794
Derivative liability, gross amounts offset (801) (598)
Derivative liability, gross amounts recognized in balance sheets 235 196
Parent Company | Not Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 741 550
Derivative liability, gross amounts recognized 900 652
Parent Company | Energy-related derivatives | Other current assets | Not Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 561 380
Parent Company | Energy-related derivatives | Other current liabilities | Not Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 575 437
Parent Company | Energy-related derivatives | Other deferred charges and assets | Not Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 180 170
Parent Company | Energy-related derivatives | Other deferred credits and liabilities | Not Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 325 215
Alabama Power    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 6 4
Derivative asset, gross amount offset (4) (4)
Derivative asset, net amounts recognized in the balance sheets 2 0
Derivative liability, gross amounts recognized 10 10
Derivative liability, gross amounts offset (4) (4)
Derivative liability, gross amounts recognized in balance sheets 6 6
Georgia Power    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 6 6
Derivative asset, gross amount offset (6) (6)
Derivative asset, net amounts recognized in the balance sheets 0 0
Derivative liability, gross amounts recognized 23 24
Derivative liability, gross amounts offset (6) (6)
Derivative liability, gross amounts recognized in balance sheets 17 18
Mississippi Power    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 3 3
Derivative asset, gross amount offset (2) (2)
Derivative asset, net amounts recognized in the balance sheets 1 1
Derivative liability, gross amounts recognized 9 9
Derivative liability, gross amounts offset (2) (2)
Derivative liability, gross amounts recognized in balance sheets 7 7
Southern Power    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 79 132
Derivative asset, gross amount offset (3) (3)
Derivative asset, net amounts recognized in the balance sheets 76 129
Derivative liability, gross amounts recognized 31 36
Derivative liability, gross amounts offset (3) (3)
Derivative liability, gross amounts recognized in balance sheets 28 33
Southern Power | Not Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 0 0
Derivative liability, gross amounts recognized 0 2
Southern Power | Energy-related derivatives | Other deferred charges and assets | Not Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 0 0
Southern Power | Energy-related derivatives | Other deferred credits and liabilities | Not Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 0 2
Southern Company Gas    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 741 554
Derivative asset, gross amount offset (508) (390)
Derivative asset, net amounts recognized in the balance sheets 233 164
Derivative liability, gross amounts recognized 909 660
Derivative liability, gross amounts offset (785) (583)
Derivative liability, gross amounts recognized in balance sheets 124 77
Collateral already posted, aggregate fair value 277 193
Weather derivative premium 8 11
Southern Company Gas | Not Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 739 549
Derivative liability, gross amounts recognized 899 649
Southern Company Gas | Energy-related derivatives    
Fair value of energy-related derivatives and interest rate derivatives    
Collateral already posted, aggregate fair value   6
Southern Company Gas | Energy-related derivatives | Other deferred charges and assets | Not Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 180 170
Southern Company Gas | Energy-related derivatives | Other deferred credits and liabilities | Not Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 325 215
Southern Company Gas | Energy-related derivatives | Assets from risk management activities | Not Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 559 379
Southern Company Gas | Energy-related derivatives | Liabilities from risk management activities | Not Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 574 434
Hedging Instruments for Regulatory Purposes | Parent Company | Energy-related derivatives | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 17 17
Derivative liability, gross amounts recognized 55 67
Hedging Instruments for Regulatory Purposes | Parent Company | Energy-related derivatives | Other current assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 8 10
Hedging Instruments for Regulatory Purposes | Parent Company | Energy-related derivatives | Other current liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 23 43
Hedging Instruments for Regulatory Purposes | Parent Company | Energy-related derivatives | Other deferred charges and assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 9 7
Hedging Instruments for Regulatory Purposes | Parent Company | Energy-related derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 26 24
Hedging Instruments for Regulatory Purposes | Parent Company | Energy-related derivatives | Assets held for sale, current | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 0 0
Hedging Instruments for Regulatory Purposes | Parent Company | Energy-related derivatives | Liabilities held for sale, current | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 6 0
Hedging Instruments for Regulatory Purposes | Alabama Power | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 6 4
Derivative liability, gross amounts recognized 10 10
Hedging Instruments for Regulatory Purposes | Alabama Power | Energy-related derivatives | Other current assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 3 2
Hedging Instruments for Regulatory Purposes | Alabama Power | Energy-related derivatives | Other current liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 4 6
Hedging Instruments for Regulatory Purposes | Alabama Power | Energy-related derivatives | Other deferred charges and assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 3 2
Hedging Instruments for Regulatory Purposes | Alabama Power | Energy-related derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 6 4
Hedging Instruments for Regulatory Purposes | Georgia Power | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 6 6
Derivative liability, gross amounts recognized 21 19
Hedging Instruments for Regulatory Purposes | Georgia Power | Energy-related derivatives | Other current assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 2 2
Hedging Instruments for Regulatory Purposes | Georgia Power | Energy-related derivatives | Other current liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 8 9
Hedging Instruments for Regulatory Purposes | Georgia Power | Energy-related derivatives | Other deferred charges and assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 4 4
Hedging Instruments for Regulatory Purposes | Georgia Power | Energy-related derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 13 10
Hedging Instruments for Regulatory Purposes | Mississippi Power | Energy-related derivatives | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 3 2
Derivative liability, gross amounts recognized 9 9
Hedging Instruments for Regulatory Purposes | Mississippi Power | Energy-related derivatives | Other current assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 1 1
Hedging Instruments for Regulatory Purposes | Mississippi Power | Energy-related derivatives | Other current liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 3 6
Hedging Instruments for Regulatory Purposes | Mississippi Power | Energy-related derivatives | Other deferred charges and assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 2 1
Hedging Instruments for Regulatory Purposes | Mississippi Power | Energy-related derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 6 3
Hedging Instruments for Regulatory Purposes | Southern Company Gas | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 2 5
Derivative liability, gross amounts recognized 9 8
Hedging Instruments for Regulatory Purposes | Southern Company Gas | Energy-related derivatives | Other deferred charges and assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 0 0
Hedging Instruments for Regulatory Purposes | Southern Company Gas | Energy-related derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 1 0
Hedging Instruments for Regulatory Purposes | Southern Company Gas | Energy-related derivatives | Assets from risk management activities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 2 5
Hedging Instruments for Regulatory Purposes | Southern Company Gas | Energy-related derivatives | Liabilities from risk management activities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 8 8
Cash Flow and Fair Value Hedging | Parent Company | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 79 133
Derivative liability, gross amounts recognized 81 75
Cash Flow and Fair Value Hedging | Parent Company | Energy-related derivatives | Other current assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 3 3
Cash Flow and Fair Value Hedging | Parent Company | Energy-related derivatives | Other current liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 7 14
Cash Flow and Fair Value Hedging | Parent Company | Energy-related derivatives | Other deferred charges and assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 1 0
Cash Flow and Fair Value Hedging | Parent Company | Energy-related derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 2 0
Cash Flow and Fair Value Hedging | Parent Company | Interest rate derivatives | Other current assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 0 1
Cash Flow and Fair Value Hedging | Parent Company | Interest rate derivatives | Other current liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 19 4
Cash Flow and Fair Value Hedging | Parent Company | Interest rate derivatives | Other deferred charges and assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 0 0
Cash Flow and Fair Value Hedging | Parent Company | Interest rate derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 30 34
Cash Flow and Fair Value Hedging | Parent Company | Foreign currency derivatives | Other current assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 0 0
Cash Flow and Fair Value Hedging | Parent Company | Foreign currency derivatives | Other current liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 23 23
Cash Flow and Fair Value Hedging | Parent Company | Foreign currency derivatives | Other deferred charges and assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 75 129
Cash Flow and Fair Value Hedging | Parent Company | Foreign currency derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 0 0
Cash Flow and Fair Value Hedging | Georgia Power | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 0 0
Derivative liability, gross amounts recognized 2 5
Cash Flow and Fair Value Hedging | Georgia Power | Interest rate derivatives | Other current assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 0 0
Cash Flow and Fair Value Hedging | Georgia Power | Interest rate derivatives | Other current liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 2 4
Cash Flow and Fair Value Hedging | Georgia Power | Interest rate derivatives | Other deferred charges and assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 0 0
Cash Flow and Fair Value Hedging | Georgia Power | Interest rate derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 0 1
Cash Flow and Fair Value Hedging | Southern Power | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 79 132
Derivative liability, gross amounts recognized 31 34
Cash Flow and Fair Value Hedging | Southern Power | Energy-related derivatives | Other current assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 3 3
Cash Flow and Fair Value Hedging | Southern Power | Energy-related derivatives | Other current liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 6 11
Cash Flow and Fair Value Hedging | Southern Power | Energy-related derivatives | Other deferred charges and assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 1 0
Cash Flow and Fair Value Hedging | Southern Power | Energy-related derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 2 0
Cash Flow and Fair Value Hedging | Southern Power | Foreign currency derivatives | Other current assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 0 0
Cash Flow and Fair Value Hedging | Southern Power | Foreign currency derivatives | Other current liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 23 23
Cash Flow and Fair Value Hedging | Southern Power | Foreign currency derivatives | Other deferred charges and assets | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 75 129
Cash Flow and Fair Value Hedging | Southern Power | Foreign currency derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized 0 0
Cash Flow and Fair Value Hedging | Southern Company Gas | Energy-related derivatives | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 0 0
Derivative liability, gross amounts recognized 1 3
Cash Flow and Fair Value Hedging | Southern Company Gas | Energy-related derivatives | Assets from risk management activities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative asset, gross amounts recognized 0 0
Cash Flow and Fair Value Hedging | Southern Company Gas | Energy-related derivatives | Liabilities from risk management activities | Designated as Hedging Instrument    
Fair value of energy-related derivatives and interest rate derivatives    
Derivative liability, gross amounts recognized $ 1 $ 3