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Derivatives - Schedule of Pre-tax Effects of Unrealized Derivative Gains (Losses) (Details) - Energy-related derivatives - USD ($)
$ in Millions
Jun. 30, 2025
Dec. 31, 2024
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) $ 55 $ (50)
Other regulatory assets, current    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) (8) (61)
Other regulatory assets, deferred    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses)   (5)
Other regulatory liabilities, current    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) 26 8
Other regulatory assets, deferred    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) 37 8
ALABAMA POWER CO    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) 24 (16)
ALABAMA POWER CO | Other regulatory assets, current    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) (3) (23)
ALABAMA POWER CO | Other regulatory assets, deferred    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses)   0
ALABAMA POWER CO | Other regulatory liabilities, current    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) 13 4
ALABAMA POWER CO | Other regulatory assets, deferred    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) 14 3
GEORGIA POWER CO    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) 18 (22)
GEORGIA POWER CO | Other regulatory assets, current    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) (1) (26)
GEORGIA POWER CO | Other regulatory assets, deferred    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses)   0
GEORGIA POWER CO | Other regulatory liabilities, current    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) 5 0
GEORGIA POWER CO | Other regulatory assets, deferred    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) 14 4
MISSISSIPPI POWER CO    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) 9 (15)
MISSISSIPPI POWER CO | Other regulatory assets, current    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) (3) (11)
MISSISSIPPI POWER CO | Other regulatory assets, deferred    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses)   (5)
MISSISSIPPI POWER CO | Other regulatory liabilities, current    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) 3 0
MISSISSIPPI POWER CO | Other regulatory assets, deferred    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) 9 1
SOUTHERN Co GAS    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) 4 3
SOUTHERN Co GAS | Other regulatory assets, current    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) (1) (1)
SOUTHERN Co GAS | Other regulatory assets, deferred    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses)   0
SOUTHERN Co GAS | Other regulatory liabilities, current    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) 5 4
SOUTHERN Co GAS | Other regulatory assets, deferred    
Derivative Instruments, Gain (Loss) [Line Items]    
Total energy-related derivative gains (losses) $ 0 $ 0