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Derivatives - Schedule of Pre-Tax Effects of Hedging on AOCI (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) Recognized in OCI on Derivatives $ (18) $ (2) $ 48 $ (7)
Cash Flow Hedging | Energy-related derivatives        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) Recognized in OCI on Derivatives (12) (7) (6) (11)
Cash Flow Hedging | Interest rate derivatives        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) Recognized in OCI on Derivatives (1) (8) 6 16
Cash Flow Hedging | Foreign currency derivatives        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) Recognized in OCI on Derivatives (6) 15 60 (4)
Fair Value Hedging | Foreign currency derivatives        
Derivative Instruments, Gain (Loss) [Line Items]        
Amount excluded from effectiveness testing recognized in earnings 1 (2) (12) (8)
GEORGIA POWER CO | Cash Flow Hedging | Interest rate derivatives        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) Recognized in OCI on Derivatives 0 1 3 17
MISSISSIPPI POWER CO | Cash Flow Hedging | Interest rate derivatives        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) Recognized in OCI on Derivatives 0 0 0 7
SOUTHERN POWER CO        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) Recognized in OCI on Derivatives (8) 13 60 (6)
SOUTHERN POWER CO | Cash Flow Hedging | Energy-related derivatives        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) Recognized in OCI on Derivatives (2) (2) 0 (2)
SOUTHERN POWER CO | Cash Flow Hedging | Foreign currency derivatives        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) Recognized in OCI on Derivatives (6) 15 60 (4)
SOUTHERN Co GAS        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) Recognized in OCI on Derivatives (11) (10) (3) (14)
SOUTHERN Co GAS | Cash Flow Hedging | Energy-related derivatives        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) Recognized in OCI on Derivatives (10) (4) (6) (9)
SOUTHERN Co GAS | Cash Flow Hedging | Interest rate derivatives        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) Recognized in OCI on Derivatives $ (1) $ (6) $ 3 $ (5)