v3.26.1
Derivatives - Narrative (Details)
MMBTU in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
USD ($)
Jun. 30, 2025
USD ($)
Jun. 30, 2026
USD ($)
MMBTU
Jun. 30, 2025
USD ($)
Dec. 31, 2025
USD ($)
Derivative [Line Items]          
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU     15.0    
Energy-related derivative hedge gain (loss) to be reclassified within twelve months $ 0   $ 0    
Gain (Loss) From Derivatives Recognized in OCI (15,000,000) $ 46,000,000 (19,000,000) $ 65,000,000  
Collateral already posted, assets, aggregate fair value 18,000,000   18,000,000    
Derivatives 377,000,000   377,000,000   $ 267,000,000
Interest rate derivatives          
Derivative [Line Items]          
Derivatives 31,000,000   31,000,000    
Interest rate derivatives | Cash Flow Hedging          
Derivative [Line Items]          
Gain (Loss) From Derivatives Recognized in OCI 0 9,000,000 0 5,000,000  
Interest rate derivatives | Cash Flow Hedging | Income Statement Location [Axis]: us-gaap:InterestAndDebtExpense          
Derivative [Line Items]          
Gain (loss) on hedges (2,000,000) (3,000,000) (5,000,000) (6,000,000)  
Interest rate derivatives | Fair Value Hedging | Income Statement Location [Axis]: us-gaap:InterestAndDebtExpense          
Derivative [Line Items]          
Gain (loss) on hedges (41,000,000) 29,000,000 (21,000,000) 69,000,000  
Energy-related derivatives | Energy-related derivatives not designated as hedging instruments | Natural gas | Income Statement Location [Axis]: us-gaap:CostOfGoodsAndServicesSold          
Derivative [Line Items]          
Derivative instruments not designated as hedging instruments, gain (loss), net 7,000,000 (14,000,000) 2,000,000 (6,000,000)  
Energy-related derivatives | Cash Flow Hedging          
Derivative [Line Items]          
Gain (Loss) From Derivatives Recognized in OCI (8,000,000) (13,000,000) 1,000,000 6,000,000  
Energy-related derivatives | Cash Flow Hedging | Natural gas | Income Statement Location [Axis]: us-gaap:CostOfGoodsAndServicesSold          
Derivative [Line Items]          
Gain (loss) on hedges (3,000,000) 1,000,000 7,000,000 0  
Foreign currency derivatives | Cash Flow Hedging          
Derivative [Line Items]          
Gain (Loss) From Derivatives Recognized in OCI (7,000,000) 47,000,000 (19,000,000) 67,000,000  
Foreign currency derivatives | Cash Flow Hedging | Income Statement Location [Axis]: us-gaap:InterestAndDebtExpense          
Derivative [Line Items]          
Gain (loss) on hedges (2,000,000) (2,000,000) (5,000,000) (5,000,000)  
Foreign currency derivatives | Cash Flow Hedging | Income Statement Location [Axis]: us-gaap:OtherNonoperatingIncomeExpense          
Derivative [Line Items]          
Gain (loss) on hedges (2,000,000) 45,000,000 (14,000,000) 67,000,000  
Foreign currency derivatives | Fair Value Hedging | Income Statement Location [Axis]: us-gaap:OtherNonoperatingIncomeExpense          
Derivative [Line Items]          
Gain (loss) on hedges (13,000,000) 115,000,000 $ (45,000,000) 155,000,000  
ALABAMA POWER CO          
Derivative [Line Items]          
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU     4.0    
Energy-related derivative hedge gain (loss) to be reclassified within twelve months 0   $ 0    
Collateral already posted, assets, aggregate fair value 0   0    
Derivatives 42,000,000   42,000,000   18,000,000
ALABAMA POWER CO | Interest rate derivatives          
Derivative [Line Items]          
Cash flow hedge gain (loss) to be reclassified within twelve months 0   0    
ALABAMA POWER CO | Energy-related derivatives | Cash Flow Hedging          
Derivative [Line Items]          
Gain (Loss) From Derivatives Recognized in OCI (2,000,000) 0 $ (2,000,000) 0  
GEORGIA POWER CO          
Derivative [Line Items]          
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU     6.0    
Derivatives 37,000,000   $ 37,000,000   19,000,000
GEORGIA POWER CO | Interest rate derivatives          
Derivative [Line Items]          
Cash flow hedge gain (loss) to be reclassified within twelve months 0   0    
GEORGIA POWER CO | Interest rate derivatives | Cash Flow Hedging          
Derivative [Line Items]          
Gain (Loss) From Derivatives Recognized in OCI 0 5,000,000 $ 0 3,000,000  
MISSISSIPPI POWER CO          
Derivative [Line Items]          
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU     2.0    
Energy-related derivative hedge gain (loss) to be reclassified within twelve months 0   $ 0    
Derivatives 27,000,000   27,000,000   14,000,000
MISSISSIPPI POWER CO | Interest rate derivatives          
Derivative [Line Items]          
Cash flow hedge gain (loss) to be reclassified within twelve months 0   $ 0    
SOUTHERN POWER CO          
Derivative [Line Items]          
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU     3.0    
Energy-related derivative hedge gain (loss) to be reclassified within twelve months 0   $ 0    
Gain (Loss) From Derivatives Recognized in OCI (9,000,000) 46,000,000 (19,000,000) 69,000,000  
Collateral already posted, assets, aggregate fair value 0   0    
Derivatives 3,000,000   3,000,000   1,000,000
SOUTHERN POWER CO | Interest rate derivatives          
Derivative [Line Items]          
Cash flow hedge gain (loss) to be reclassified within twelve months 0   0    
SOUTHERN POWER CO | Energy-related derivatives          
Derivative [Line Items]          
Derivatives 0   0    
SOUTHERN POWER CO | Energy-related derivatives | Cash Flow Hedging          
Derivative [Line Items]          
Gain (Loss) From Derivatives Recognized in OCI (2,000,000) (1,000,000) 0 2,000,000  
SOUTHERN POWER CO | Foreign currency derivatives | Cash Flow Hedging          
Derivative [Line Items]          
Gain (Loss) From Derivatives Recognized in OCI (7,000,000) 47,000,000 (19,000,000) 67,000,000  
SOUTHERN POWER CO | Foreign currency derivatives | Cash Flow Hedging | Income Statement Location [Axis]: us-gaap:InterestAndDebtExpense          
Derivative [Line Items]          
Gain (loss) on hedges (2,000,000) (2,000,000) (5,000,000) (5,000,000)  
SOUTHERN POWER CO | Foreign currency derivatives | Cash Flow Hedging | Income Statement Location [Axis]: us-gaap:OtherNonoperatingIncomeExpense          
Derivative [Line Items]          
Gain (loss) on hedges (2,000,000) 45,000,000 (14,000,000) 67,000,000  
Registrants | Derivative Counterparties          
Derivative [Line Items]          
Collateral already posted, assets, aggregate fair value 0   0    
SOUTHERN Co GAS          
Derivative [Line Items]          
Energy-related derivative hedge gain (loss) to be reclassified within twelve months 0   0    
Gain (Loss) From Derivatives Recognized in OCI (4,000,000) (8,000,000) 3,000,000 8,000,000  
Collateral already posted, assets, aggregate fair value 18,000,000   18,000,000   33,000,000
Derivatives 66,000,000   66,000,000   $ 65,000,000
SOUTHERN Co GAS | Interest rate derivatives          
Derivative [Line Items]          
Cash flow hedge gain (loss) to be reclassified within twelve months 0   0    
SOUTHERN Co GAS | Interest rate derivatives | Cash Flow Hedging          
Derivative [Line Items]          
Gain (Loss) From Derivatives Recognized in OCI 0 4,000,000 0 4,000,000  
SOUTHERN Co GAS | Interest rate derivatives | Fair Value Hedging | Income Statement Location [Axis]: us-gaap:InterestAndDebtExpense          
Derivative [Line Items]          
Gain (loss) on hedges (32,000,000) 3,000,000 (3,000,000) 21,000,000  
SOUTHERN Co GAS | Energy-related derivatives | Cash Flow Hedging          
Derivative [Line Items]          
Gain (Loss) From Derivatives Recognized in OCI (4,000,000) (12,000,000) 3,000,000 4,000,000  
SOUTHERN Co GAS | Energy-related derivatives | Cash Flow Hedging | Natural gas | Income Statement Location [Axis]: us-gaap:CostOfGoodsAndServicesSold          
Derivative [Line Items]          
Gain (loss) on hedges (3,000,000) $ 1,000,000 7,000,000 $ 0  
Traditional Electric Operating Companies | Energy-related derivatives          
Derivative [Line Items]          
Derivatives $ 0   $ 0