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Derivatives - Schedule of Derivative Category and Balance Sheet Location (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized $ 90 $ 93
Gross amounts offset (53) (21)
Derivative asset, net amounts recognized in the balance sheets 37 72
Derivative liability, gross amount recognized 401 321
Gross amounts offset (75) (54)
Derivative liability, net amounts recognized in the balance sheets 326 267
Collateral already posted, assets, aggregate fair value 22  
Interest rate derivatives    
Derivatives, Fair Value [Line Items]    
Derivative liability, net amounts recognized in the balance sheets 26  
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 5 6
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 5 6
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 69 55
Derivative liability, gross amount recognized 147 99
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 35 24
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 91 64
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 34 31
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 56 35
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 16 32
Derivative liability, gross amount recognized 249 216
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 1
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 8 6
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 2 2
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 1
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 8
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 49 48
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 142 139
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 5 17
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 22 22
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 4
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 28 0
ALABAMA POWER CO    
Derivatives, Fair Value [Line Items]    
Gross amounts offset (23) (13)
Derivative asset, net amounts recognized in the balance sheets 2 6
Gross amounts offset (23) (13)
Derivative liability, net amounts recognized in the balance sheets 25 18
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 25 19
Derivative liability, gross amount recognized 48 31
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 12 9
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 26 18
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 13 10
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 22 13
GEORGIA POWER CO    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 25 18
Gross amounts offset (21) (14)
Derivative asset, net amounts recognized in the balance sheets 4 4
Derivative liability, gross amount recognized 49 33
Gross amounts offset (21) (14)
Derivative liability, net amounts recognized in the balance sheets 28 19
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 3 1
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 0
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 22 17
Derivative liability, gross amount recognized 49 33
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 13 7
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 32 23
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 9 10
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 17 10
MISSISSIPPI POWER CO    
Derivatives, Fair Value [Line Items]    
Gross amounts offset (18) (13)
Derivative asset, net amounts recognized in the balance sheets 1 1
Gross amounts offset (18) (13)
Derivative liability, net amounts recognized in the balance sheets 20 14
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 19 14
Derivative liability, gross amount recognized 38 27
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 7 3
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 21 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 12 11
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 17 12
SOUTHERN POWER CO    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 9 21
Gross amounts offset (1) 0
Derivative asset, net amounts recognized in the balance sheets 8 21
Derivative liability, gross amount recognized 3 1
Gross amounts offset (1) 0
Derivative liability, net amounts recognized in the balance sheets 2 1
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 | Interest rate derivatives    
Derivatives, Fair Value [Line Items]    
Derivative liability, net amounts recognized in the balance sheets 0  
SOUTHERN 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 1 1
SOUTHERN 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 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    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 8 20
Derivative liability, gross amount recognized 2 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 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 2 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 deferred charges and assets    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 2 2
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 5 17
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 0
SOUTHERN Co GAS    
Derivatives, Fair Value [Line Items]    
Derivative asset, gross amount recognized 5 9
Gross amounts offset 10 19
Derivative asset, net amounts recognized in the balance sheets 15 28
Derivative liability, gross amount recognized 77 79
Gross amounts offset (12) (14)
Derivative liability, net amounts recognized in the balance sheets 65 65
Collateral already posted, assets, aggregate fair value 22 33
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 1 4
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 4 6
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 3 5
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 12 8
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 1 0
Derivative liability, gross amount recognized 61 65
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 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 | Energy-related derivatives | Other current liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 6 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 | Energy-related 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 | Energy-related derivatives | Other deferred credits and liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liability, gross amount recognized 0 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 | 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 12 13
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 $ 46