v3.25.0.1
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of AOCI (Loss) Balances, Net of Tax Effects (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Beginning balance $ 35,225 $ 34,532 $ 32,276
Total other comprehensive income 99 (10) 71
Ending balance 36,674 35,225 34,532
Other 19 (5) (6)
Qualifying Hedges      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Beginning balance (121) (149) (162)
Total other comprehensive income 75 28 13
Ending balance (46) (121) (149)
Pension and Other Postretirement Benefit Plans      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Beginning balance (56) (18) (76)
Total other comprehensive income 24 (38) 58
Ending balance (32) (56) (18)
Accumulated Other Comprehensive Income (Loss)(*)      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Beginning balance (177) (167) (237)
Total other comprehensive income 99 (10) 71
Ending balance (78) (177) (167)
Other 0   (1)
Southern Power      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Beginning balance 6,698 6,916 6,598
Total other comprehensive income 15 1 10
Ending balance 6,682 6,698 6,916
Other   (1) (1)
Southern Power | Qualifying Hedges      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Beginning balance (1) (9) 1
Total other comprehensive income 8 8 (10)
Ending balance 7 (1) (9)
Southern Power | Pension and Other Postretirement Benefit Plans      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Beginning balance (16) (9) (29)
Total other comprehensive income 7 (7) 20
Ending balance (9) (16) (9)
Southern Power | Accumulated Other Comprehensive Income (Loss)(*)      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Beginning balance (17) (18) (27)
Total other comprehensive income 15 1 10
Ending balance (2) (17) (18)
Other     (1)
Southern Company Gas      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Total other comprehensive income 32 (15) 7
Other (1)    
Southern Company Gas | Qualifying Hedges      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Beginning balance (24) (25) (14)
Total other comprehensive income 21 1 (11)
Ending balance (3) (24) (25)
Southern Company Gas | Pension and Other Postretirement Benefit Plans      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Beginning balance 40 56 38
Total other comprehensive income 11 (16) 18
Ending balance 51 40 56
Southern Company Gas | Accumulated Other Comprehensive Income (Loss)(*)      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Beginning balance 16 31 24
Total other comprehensive income 32 (15) 7
Ending balance $ 48 $ 16 $ 31