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Regulatory Matters - Schedule of Cost Recovery Clauses (Details) - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
ALABAMA POWER CO | Other regulatory assets, current    
Loss Contingencies [Line Items]    
Rate ECR $ 14 $ 0
ALABAMA POWER CO | Other regulatory assets, deferred    
Loss Contingencies [Line Items]    
Rate ECR 69 0
ALABAMA POWER CO | Other regulatory liabilities, current    
Loss Contingencies [Line Items]    
Rate ECR 0 29
GEORGIA POWER CO | Receivables – under recovered retail fuel clause revenues    
Loss Contingencies [Line Items]    
Fuel Cost Recovery 487 713
GEORGIA POWER CO | Deferred under recovered retail fuel clause revenues    
Loss Contingencies [Line Items]    
Fuel Cost Recovery 197 453
MISSISSIPPI POWER CO | Wholesale MB    
Loss Contingencies [Line Items]    
Fuel Cost Recovery 0 0
MISSISSIPPI POWER CO | Deferred under recovered retail fuel clause revenues    
Loss Contingencies [Line Items]    
Fuel Cost Recovery 0 32
MISSISSIPPI POWER CO | Receivables – customer accounts, net    
Loss Contingencies [Line Items]    
Fuel Cost Recovery 30 0
MISSISSIPPI POWER CO | Over recovered retail fuel clause revenues    
Loss Contingencies [Line Items]    
Fuel Cost Recovery 0 32
MISSISSIPPI POWER CO | Other current liabilities | Wholesale MRA    
Loss Contingencies [Line Items]    
Fuel Cost Recovery 0 19
SOUTHERN Co GAS | Natural gas cost over recovery    
Loss Contingencies [Line Items]    
Natural gas cost under recovery $ 163 $ 193