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RETIREMENT BENEFITS - Components of Net Periodic Benefit Cost and Estimated Future Benefit Payments (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Pension plans      
Components of net periodic      
Service cost $ 412 $ 434 $ 376
Interest cost 408 346 432
Expected return on plan assets (1,265) (1,191) (1,100)
Recognized net loss 240 314 269
Net amortization 0 1 1
Prior service cost 0 0 0
Total change (205) (96) (22)
Benefit payments:      
2023 734    
2024 735    
2025 760    
2026 784    
2027 806    
2028 to 2032 4,262    
Other postretirement benefit plans      
Components of net periodic      
Service cost 23 24 22
Interest cost 42 35 54
Expected return on plan assets (80) (76) (72)
Prior service cost (1) 2 1
Total change (16) (15) 5
Benefit payments:      
2023 115    
2024 110    
2025 114    
2026 113    
2027 113    
2028 to 2032 551    
Alabama Power | Pension plans      
Components of net periodic      
Service cost 99 102 89
Interest cost 96 82 100
Expected return on plan assets (306) (287) (264)
Recognized net loss 62 82 71
Net amortization 1 1 1
Prior service cost 0 0 0
Total change (48) (20) (3)
Benefit payments:      
2023 155    
2024 160    
2025 167    
2026 173    
2027 178    
2028 to 2032 952    
Alabama Power | Other postretirement benefit plans      
Components of net periodic      
Service cost 6 6 6
Interest cost 10 9 13
Expected return on plan assets (32) (30) (29)
Prior service cost 0 0 0
Total change (16) (15) (10)
Benefit payments:      
2023 25    
2024 24    
2025 26    
2026 26    
2027 26    
2028 to 2032 130    
Georgia Power | Pension plans      
Components of net periodic      
Service cost 103 112 96
Interest cost 123 104 133
Expected return on plan assets (399) (375) (347)
Recognized net loss 75 100 86
Net amortization 1 1 1
Prior service cost 0 0 0
Total change (97) (58) (31)
Benefit payments:      
2023 230    
2024 236    
2025 243    
2026 248    
2027 252    
2028 to 2032 1,304    
Georgia Power | Other postretirement benefit plans      
Components of net periodic      
Service cost 6 7 6
Interest cost 15 12 20
Expected return on plan assets (28) (26) (26)
Prior service cost 2 2 2
Total change (5) (5) 2
Benefit payments:      
2023 41    
2024 39    
2025 41    
2026 41    
2027 41    
2028 to 2032 199    
Mississippi Power | Pension plans      
Components of net periodic      
Service cost 17 18 15
Interest cost 18 16 20
Expected return on plan assets (57) (55) (51)
Recognized net loss 11 15 13
Net amortization 0 0 0
Prior service cost 0 0 0
Total change (11) (6) (3)
Benefit payments:      
2023 32    
2024 33    
2025 34    
2026 35    
2027 36    
2028 to 2032 192    
Mississippi Power | Other postretirement benefit plans      
Components of net periodic      
Service cost 1 1 1
Interest cost 2 1 2
Expected return on plan assets (2) (1) (1)
Prior service cost 0 0 0
Total change 1 1 2
Benefit payments:      
2023 5    
2024 5    
2025 5    
2026 5    
2027 5    
2028 to 2032 22    
Southern Power | Pension plans      
Components of net periodic      
Service cost 9 10 8
Interest cost 6 5 6
Expected return on plan assets (15) (14) (13)
Recognized net loss 2 3 2
Net amortization 0 0 0
Prior service cost 0 0 0
Total change 2 4 3
Benefit payments:      
2023 6    
2024 7    
2025 7    
2026 7    
2027 8    
2028 to 2032 43    
Southern Power | Other postretirement benefit plans      
Components of net periodic      
Service cost 0 0 1
Interest cost 0 0 0
Expected return on plan assets 1 1 0
Prior service cost 0 0 0
Total change 1 1 1
Benefit payments:      
2023 1    
2024 1    
2025 1    
2026 1    
2027 1    
2028 to 2032 1    
Southern Company Gas | Pension plans      
Components of net periodic      
Service cost 34 37 33
Interest cost 28 24 31
Expected return on plan assets (91) (86) (75)
Recognized net loss 8 13 6
Net amortization 15 15 15
Prior service cost (3) (3) (3)
Total change (9) 0 7
Benefit payments:      
2023 83    
2024 57    
2025 58    
2026 60    
2027 61    
2028 to 2032 323    
Southern Company Gas | Other postretirement benefit plans      
Components of net periodic      
Service cost 1 2 2
Interest cost 5 4 7
Expected return on plan assets (9) (10) (10)
Prior service cost 6 6 6
Total change 3 $ 2 $ 5
Benefit payments:      
2023 18    
2024 17    
2025 17    
2026 16    
2027 16    
2028 to 2032 $ 68