v3.26.1
Derivatives - Schedule of Pre-Tax Effects of Cash Flow and Fair Value Hedging on Income (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Income Statement Location [Axis]: us-gaap:OtherNonoperatingIncomeExpense        
Derivative [Line Items]        
Amount excluded from effectiveness testing recognized in earnings $ 0 $ (3) $ 1 $ 13
Cash Flow Hedging | Energy-related derivatives | Income Statement Location [Axis]: us-gaap:CostOfGoodsAndServicesSold | Fuel        
Derivative [Line Items]        
Gain (loss) on hedges (1) 0 2 1
Cash Flow Hedging | Energy-related derivatives | Income Statement Location [Axis]: us-gaap:CostOfGoodsAndServicesSold | Natural gas        
Derivative [Line Items]        
Gain (loss) on hedges (3) 1 7 0
Cash Flow Hedging | Interest rate derivatives | Income Statement Location [Axis]: us-gaap:InterestAndDebtExpense        
Derivative [Line Items]        
Gain (loss) on hedges (2) (3) (5) (6)
Cash Flow Hedging | Foreign currency derivatives | Income Statement Location [Axis]: us-gaap:InterestAndDebtExpense        
Derivative [Line Items]        
Gain (loss) on hedges (2) (2) (5) (5)
Cash Flow Hedging | Foreign currency derivatives | Income Statement Location [Axis]: us-gaap:OtherNonoperatingIncomeExpense        
Derivative [Line Items]        
Gain (loss) on hedges (2) 45 (14) 67
Fair Value Hedging | Interest rate derivatives | Income Statement Location [Axis]: us-gaap:InterestAndDebtExpense        
Derivative [Line Items]        
Gain (loss) on hedges (41) 29 (21) 69
Fair Value Hedging | Foreign currency derivatives        
Derivative [Line Items]        
Amount excluded from effectiveness testing recognized in earnings 0 3 (1) (13)
Fair Value Hedging | Foreign currency derivatives | Income Statement Location [Axis]: us-gaap:OtherNonoperatingIncomeExpense        
Derivative [Line Items]        
Gain (loss) on hedges (13) 115 (45) 155
SOUTHERN POWER CO | Cash Flow Hedging | Energy-related derivatives | Income Statement Location [Axis]: us-gaap:CostOfGoodsAndServicesSold | Fuel        
Derivative [Line Items]        
Gain (loss) on hedges (1) 0 2 1
SOUTHERN POWER CO | Cash Flow Hedging | Foreign currency derivatives | Income Statement Location [Axis]: us-gaap:InterestAndDebtExpense        
Derivative [Line Items]        
Gain (loss) on hedges (2) (2) (5) (5)
SOUTHERN POWER CO | Cash Flow Hedging | Foreign currency derivatives | Income Statement Location [Axis]: us-gaap:OtherNonoperatingIncomeExpense        
Derivative [Line Items]        
Gain (loss) on hedges (2) 45 (14) 67
SOUTHERN Co GAS | Cash Flow Hedging | Energy-related derivatives | Income Statement Location [Axis]: us-gaap:CostOfGoodsAndServicesSold | Natural gas        
Derivative [Line Items]        
Gain (loss) on hedges (3) 1 7 0
SOUTHERN Co GAS | Fair Value Hedging | Interest rate derivatives | Income Statement Location [Axis]: us-gaap:InterestAndDebtExpense        
Derivative [Line Items]        
Gain (loss) on hedges $ (32) $ 3 $ (3) $ 21