v3.25.0.1
RETIREMENT BENEFITS - Components of Accumulated OCI (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning balance $ 35,225 $ 34,532 $ 32,276
Total other comprehensive income (loss) 99 (10) 71
Ending balance 36,674 35,225 34,532
Pension and Other Postretirement Benefit Plans      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning balance (56) (18) (76)
Total other comprehensive income (loss) 24 (38) 58
Ending balance (32) (56) (18)
Pension plans      
Defined Benefit Plan Disclosure [Line Items]      
Prior service cost (1) (1)  
Net loss 53 80  
AOCI 52 79  
Pension plans | Pension and Other Postretirement Benefit Plans      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning balance 79 24  
Reclassification adjustments 2 (7)  
Total other comprehensive income (loss) (27) 55  
Ending balance 52 79 24
Pension plans | Net loss      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Net loss (29) 62  
Reclassification adjustments 1 (8)  
Other Postretirement Benefits Plan      
Defined Benefit Plan Disclosure [Line Items]      
Prior service cost   1  
Net loss (14) (10)  
AOCI (14) (9)  
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Reclassification adjustments 3 7  
Other Postretirement Benefits Plan | Pension and Other Postretirement Benefit Plans      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning balance (9) (4)  
Total other comprehensive income (loss) (5) (5)  
Ending balance (14) (9) (4)
Other Postretirement Benefits Plan | Net loss      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Net loss (8) (12)  
Southern Power      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning balance 6,698 6,916 6,598
Total other comprehensive income (loss) 15 1 10
Ending balance 6,682 6,698 6,916
Southern Power | Pension and Other Postretirement Benefit Plans      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning balance (16) (9) (29)
Total other comprehensive income (loss) 7 (7) 20
Ending balance (9) (16) (9)
Southern Power | Pension plans      
Defined Benefit Plan Disclosure [Line Items]      
Prior service cost 0 0  
Net loss 11 20  
AOCI 11 20  
Southern Power | Pension plans | Pension and Other Postretirement Benefit Plans      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning balance 20 11  
Reclassification adjustments 0 0  
Total other comprehensive income (loss) (9) 9  
Ending balance 11 20 11
Southern Power | Pension plans | Net loss      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Net loss (9) 9  
Reclassification adjustments 0 0  
Southern Power | Other Postretirement Benefits Plan      
Defined Benefit Plan Disclosure [Line Items]      
Prior service cost   0  
Net loss 0 1  
AOCI 0 1  
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Reclassification adjustments 0 0  
Southern Power | Other Postretirement Benefits Plan | Pension and Other Postretirement Benefit Plans      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning balance 1 0  
Total other comprehensive income (loss) (1) 1  
Ending balance 0 1 0
Southern Power | Other Postretirement Benefits Plan | Net loss      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Net loss (1) 1  
Southern Company Gas      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Total other comprehensive income (loss) 32 (15) 7
Southern Company Gas | Pension and Other Postretirement Benefit Plans      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning balance 40 56 38
Total other comprehensive income (loss) 11 (16) 18
Ending balance 51 40 56
Southern Company Gas | Pension plans      
Defined Benefit Plan Disclosure [Line Items]      
Prior service cost (1) (2)  
Net loss (53) (43)  
AOCI (54) (45)  
Southern Company Gas | Pension plans | Pension and Other Postretirement Benefit Plans      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning balance (45) (75)  
Reclassification adjustments 2 1  
Total other comprehensive income (loss) (9) 30  
Ending balance (54) (45) (75)
Southern Company Gas | Pension plans | Net loss      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Net loss (11) 29  
Reclassification adjustments 0 0  
Southern Company Gas | Other Postretirement Benefits Plan      
Defined Benefit Plan Disclosure [Line Items]      
Prior service cost   0  
Net loss (15) (10)  
AOCI (15) (10)  
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Reclassification adjustments 0 (8)  
Southern Company Gas | Other Postretirement Benefits Plan | Pension and Other Postretirement Benefit Plans      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning balance (10) (2)  
Total other comprehensive income (loss) (5) (8)  
Ending balance (15) (10) $ (2)
Southern Company Gas | Other Postretirement Benefits Plan | Net loss      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Net loss $ (5) $ 0