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Derivatives - Schedule of Derivative Category and Balance Sheet Location (Details) - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized $ 142 $ 89
Gross amounts offset (54) (44)
Derivative asset, net amounts recognized in the balance sheets 88 45
Derivative liability, gross amount recognized 301 615
Gross amounts offset (63) (61)
Derivative liability, net amounts recognized in the balance sheets 238 554
Collateral already posted, assets, aggregate fair value 10  
Interest rate derivatives    
Derivatives, Fair Value [Line Items]    
Derivative liability, net amounts recognized in the balance sheets 20  
Energy-related derivatives not designated as hedging instruments    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 13 6
Derivative liability, gross amount recognized 7 3
Energy-related derivatives not designated as hedging instruments | Energy-related derivatives | Assets from risk management activities    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 13 5
Energy-related derivatives not designated as hedging instruments | Energy-related derivatives | Liabilities from risk management activities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 7 3
Energy-related derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred charges and assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 0 1
Energy-related derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred credits and liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 0 0
Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 85 75
Derivative liability, gross amount recognized 76 122
Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Assets from risk management activities    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 34 33
Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Liabilities from risk management activities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 44 82
Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred charges and assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 51 42
Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred credits and liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 32 40
Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 44 8
Derivative liability, gross amount recognized 218 490
Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Assets from risk management activities    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 2 4
Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Liabilities from risk management activities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 6 3
Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred charges and assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 4 4
Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred credits and liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 0 0
Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Assets from risk management activities    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 7 0
Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Liabilities from risk management activities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 53 61
Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other deferred charges and assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 0 0
Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other deferred credits and liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 138 208
Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Assets from risk management activities    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 20 0
Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Liabilities from risk management activities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 21 36
Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other deferred charges and assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 11 0
Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other deferred credits and liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 0 182
ALABAMA POWER CO    
Derivatives, Fair Value [Line Items]    
Gross amounts offset (17) (19)
Derivative asset, net amounts recognized in the balance sheets 14 7
Gross amounts offset (17) (19)
Derivative liability, net amounts recognized in the balance sheets 8 23
Collateral already posted, assets, aggregate fair value 0  
ALABAMA POWER CO | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 31 26
Derivative liability, gross amount recognized 25 42
ALABAMA POWER CO | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 13 11
ALABAMA POWER CO | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 13 30
ALABAMA POWER CO | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred charges and assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 18 15
ALABAMA POWER CO | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred credits and liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 12 12
GEORGIA POWER CO    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 27 19
Gross amounts offset (16) (15)
Derivative asset, net amounts recognized in the balance sheets 11 4
Derivative liability, gross amount recognized 24 42
Gross amounts offset (16) (15)
Derivative liability, net amounts recognized in the balance sheets 8 27
GEORGIA POWER CO | Energy-related derivatives not designated as hedging instruments | Energy-related derivatives | Other current assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 2 0
GEORGIA POWER CO | Energy-related derivatives not designated as hedging instruments | Energy-related derivatives | Other current liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 0 1
GEORGIA POWER CO | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 25 19
Derivative liability, gross amount recognized 24 41
GEORGIA POWER CO | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Assets from risk management activities    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 8 6
GEORGIA POWER CO | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 15 32
GEORGIA POWER CO | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred charges and assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 17 13
GEORGIA POWER CO | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred credits and liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 9 9
MISSISSIPPI POWER CO    
Derivatives, Fair Value [Line Items]    
Gross amounts offset (15) (17)
Derivative asset, net amounts recognized in the balance sheets 5 2
Gross amounts offset (15) (17)
Derivative liability, net amounts recognized in the balance sheets 8 17
MISSISSIPPI POWER CO | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 20 19
Derivative liability, gross amount recognized 23 34
MISSISSIPPI POWER CO | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Assets from risk management activities    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 4 5
MISSISSIPPI POWER CO | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 12 15
MISSISSIPPI POWER CO | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred charges and assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 16 14
MISSISSIPPI POWER CO | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred credits and liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 11 19
SOUTHERN POWER CO    
Derivatives, Fair Value [Line Items]    
Derivative asset, net amounts recognized in the balance sheets 24 4
Derivative liability, net amounts recognized in the balance sheets 1 51
Collateral already posted, assets, aggregate fair value 0  
SOUTHERN POWER CO | Energy-related derivatives    
Derivatives, Fair Value [Line Items]    
Derivative liability, net amounts recognized in the balance sheets 0  
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 24 4
Derivative liability, gross amount recognized 1 51
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 1 1
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 1 0
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred charges and assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 3 3
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred credits and liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 0 0
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other current assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 20 0
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other current liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 0 11
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other deferred charges and assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 0 0
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other deferred credits and liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 0 40
SOUTHERN Co GAS    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 22 21
Gross amounts offset (6) 7
Derivative asset, net amounts recognized in the balance sheets 16 28
Derivative liability, gross amount recognized 72 94
Gross amounts offset (15) (10)
Derivative liability, net amounts recognized in the balance sheets 57 84
Collateral already posted, assets, aggregate fair value 10 17
SOUTHERN Co GAS | Energy-related derivatives not designated as hedging instruments    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 11 6
Derivative liability, gross amount recognized 7 2
SOUTHERN Co GAS | Energy-related derivatives not designated as hedging instruments | Energy-related derivatives | Other current assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 11 5
SOUTHERN Co GAS | Energy-related derivatives not designated as hedging instruments | Energy-related derivatives | Other current liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 7 2
SOUTHERN Co GAS | Energy-related derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred charges and assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 0 1
SOUTHERN Co GAS | Energy-related derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred credits and liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 0 0
SOUTHERN Co GAS | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 9 11
SOUTHERN Co GAS | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 4 5
SOUTHERN Co GAS | Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 2 4
Derivative liability, gross amount recognized 61 87
SOUTHERN Co GAS | Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 1 3
SOUTHERN Co GAS | Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 5 3
SOUTHERN Co GAS | Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred charges and assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 1 1
SOUTHERN Co GAS | Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred credits and liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 0 0
SOUTHERN Co GAS | Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other current assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 0 0
SOUTHERN Co GAS | Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other current liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 13 17
SOUTHERN Co GAS | Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other deferred charges and assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 0 0
SOUTHERN Co GAS | Derivatives designated as hedging instruments in cash flow and fair value hedges | Energy-related derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other deferred credits and liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized $ 43 $ 67