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Regulatory Matters - Schedule of Cost Recovery Clauses (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
ALABAMA POWER CO | Other regulatory assets, deferred    
Loss Contingencies [Line Items]    
Rate ECR $ 200 $ 146
ALABAMA POWER CO | Other regulatory liabilities, deferred    
Loss Contingencies [Line Items]    
Liability for Unpaid Claims and Claims Adjustment Expense, Net 52 60
GEORGIA POWER CO | Other regulatory assets, current | Property Damage Reserve Asset    
Loss Contingencies [Line Items]    
Regulatory asset balance related to storm damage 31 31
GEORGIA POWER CO | Other regulatory assets, deferred | Property Damage Reserve Asset    
Loss Contingencies [Line Items]    
Regulatory asset balance related to storm damage 962 880
GEORGIA POWER CO | Receivables – under recovered retail fuel clause revenues    
Loss Contingencies [Line Items]    
Fuel cost recovery 234 310
GEORGIA POWER CO | Deferred under recovered retail fuel clause revenues    
Loss Contingencies [Line Items]    
Fuel cost recovery 210 212
MISSISSIPPI POWER CO | Wholesale MB    
Loss Contingencies [Line Items]    
Fuel cost recovery 0 0
MISSISSIPPI POWER CO | Other regulatory assets, deferred | Retail electric revenues    
Loss Contingencies [Line Items]    
Property damage reserve 57 57
MISSISSIPPI POWER CO | Deferred under recovered retail fuel clause revenues    
Loss Contingencies [Line Items]    
Fuel cost recovery 0 40
MISSISSIPPI POWER CO | Receivables – customer accounts, net    
Loss Contingencies [Line Items]    
Fuel cost recovery 55 0
MISSISSIPPI POWER CO | Other current assets | Wholesale MRA    
Loss Contingencies [Line Items]    
Fuel cost recovery 9 6
SOUTHERN Co GAS | Natural gas cost over recovery    
Loss Contingencies [Line Items]    
Natural gas cost under recovery $ 131 $ 158