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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, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Pension plans |  |  |
Components of net periodic |  |  |
Service cost | $ 292 | $ 275 | $ 412
Interest cost | 635 | 626 | 408
Expected return on plan assets | (1,263) | (1,229) | (1,265)
Recognized net loss(*) | 55 | 32 | 240
Net amortization(*) | 0 | 0 | 0
Prior service cost(*) | 0 | 0 | 0
Total change | (281) | (296) | (205)
Benefit payments: |  |  |
2025 | 773 |  |
2026 | 801 |  |
2027 | 823 |  |
2028 | 842 |  |
2029 | 862 |  |
2030 to 2034 | 4,529 |  |
Unamortized amounts | 20 | 17 | 21
Other Postretirement Benefits Plan |  |  |
Components of net periodic |  |  |
Service cost | 15 | 15 | 23
Interest cost | 65 | 70 | 42
Expected return on plan assets | (89) | (83) | (80)
Prior service cost(*) | (13) | (11) | (1)
Total change | (22) | (9) | (16)
Benefit payments: |  |  |
2025 | 112 |  |
2026 | 112 |  |
2027 | 113 |  |
2028 | 114 |  |
2029 | 114 |  |
2030 to 2034 | 558 |  |
Unamortized amounts | 8 |  |
Alabama Power | Pension plans |  |  |
Components of net periodic |  |  |
Service cost | 68 | 64 | 99
Interest cost | 148 | 145 | 96
Expected return on plan assets | (307) | (297) | (306)
Recognized net loss(*) | 16 | 9 | 62
Net amortization(*) | 1 | 1 | 1
Prior service cost(*) | 0 | 0 | 0
Total change | (74) | (78) | (48)
Benefit payments: |  |  |
2025 | 170 |  |
2026 | 177 |  |
2027 | 183 |  |
2028 | 187 |  |
2029 | 192 |  |
2030 to 2034 | 1,013 |  |
Alabama Power | Other Postretirement Benefits Plan |  |  |
Components of net periodic |  |  |
Service cost | 4 | 4 | 6
Interest cost | 16 | 17 | 10
Expected return on plan assets | (35) | (33) | (32)
Prior service cost(*) | (3) | (3) | 0
Total change | (18) | (15) | (16)
Benefit payments: |  |  |
2025 | 24 |  |
2026 | 25 |  |
2027 | 26 |  |
2028 | 26 |  |
2029 | 27 |  |
2030 to 2034 | 133 |  |
Georgia Power | Pension plans |  |  |
Components of net periodic |  |  |
Service cost | 70 | 68 | 103
Interest cost | 191 | 191 | 123
Expected return on plan assets | (393) | (385) | (399)
Recognized net loss(*) | 19 | 13 | 75
Net amortization(*) | 1 | 1 | 1
Prior service cost(*) | 0 | 0 | 0
Total change | (112) | (112) | (97)
Benefit payments: |  |  |
2025 | 245 |  |
2026 | 250 |  |
2027 | 254 |  |
2028 | 258 |  |
2029 | 262 |  |
2030 to 2034 | 1,333 |  |
Georgia Power | Other Postretirement Benefits Plan |  |  |
Components of net periodic |  |  |
Service cost | 4 | 4 | 6
Interest cost | 23 | 25 | 15
Expected return on plan assets | (32) | (29) | (28)
Prior service cost(*) | (4) | (3) | 2
Total change | (9) | (3) | (5)
Benefit payments: |  |  |
2025 | 40 |  |
2026 | 40 |  |
2027 | 41 |  |
2028 | 41 |  |
2029 | 42 |  |
2030 to 2034 | 205 |  |
Mississippi Power | Pension plans |  |  |
Components of net periodic |  |  |
Service cost | 12 | 11 | 17
Interest cost | 29 | 28 | 18
Expected return on plan assets | (58) | (56) | (57)
Recognized net loss(*) | 3 | 2 | 11
Net amortization(*) | 0 | 0 | 0
Prior service cost(*) | 0 | 0 | 0
Total change | (14) | (15) | (11)
Benefit payments: |  |  |
2025 | 34 |  |
2026 | 36 |  |
2027 | 37 |  |
2028 | 38 |  |
2029 | 38 |  |
2030 to 2034 | 204 |  |
Mississippi Power | Other Postretirement Benefits Plan |  |  |
Components of net periodic |  |  |
Service cost | 1 | 1 | 1
Interest cost | 3 | 3 | 2
Expected return on plan assets | (3) | (3) | (2)
Prior service cost(*) | 0 | 0 | 0
Total change | 1 | 1 | 1
Benefit payments: |  |  |
2025 | 5 |  |
2026 | 5 |  |
2027 | 5 |  |
2028 | 5 |  |
2029 | 5 |  |
2030 to 2034 | 22 |  |
Southern Power | Pension plans |  |  |
Components of net periodic |  |  |
Service cost | 7 | 6 | 9
Interest cost | 9 | 8 | 6
Expected return on plan assets | (17) | (15) | (15)
Recognized net loss(*) | 0 | 0 | 2
Net amortization(*) | 0 | 0 | 0
Prior service cost(*) | 0 | 0 | 0
Total change | (1) | (1) | 2
Benefit payments: |  |  |
2025 | 7 |  |
2026 | 8 |  |
2027 | 8 |  |
2028 | 7 |  |
2029 | 8 |  |
2030 to 2034 | 51 |  |
Southern Power | Other Postretirement Benefits Plan |  |  |
Components of net periodic |  |  |
Service cost | 0 | 0 | 0
Interest cost | 0 | 0 | 0
Expected return on plan assets | 1 | 1 | 1
Prior service cost(*) | 0 | 0 | 0
Total change | 1 | 1 | 1
Benefit payments: |  |  |
2025 | 1 |  |
2026 | 1 |  |
2027 | 1 |  |
2028 | 1 |  |
2029 | 1 |  |
2030 to 2034 | 1 |  |
Southern Company Gas | Pension plans |  |  |
Components of net periodic |  |  |
Service cost | 28 | 24 | 34
Interest cost | 42 | 42 | 28
Expected return on plan assets | (85) | (85) | (91)
Recognized net loss(*) | 0 | (5) | 8
Net amortization(*) | 15 | 15 | 15
Prior service cost(*) | (3) | (3) | (3)
Total change | (3) | (12) | (9)
Benefit payments: |  |  |
2025 | 58 |  |
2026 | 60 |  |
2027 | 62 |  |
2028 | 64 |  |
2029 | 66 |  |
2030 to 2034 | 346 |  |
Southern Company Gas | Other Postretirement Benefits Plan |  |  |
Components of net periodic |  |  |
Service cost | 1 | 1 | 1
Interest cost | 8 | 9 | 5
Expected return on plan assets | (13) | (10) | (9)
Prior service cost(*) | 6 | 6 | 6
Total change | 2 | $ 6 | $ 3
Benefit payments: |  |  |
2025 | 16 |  |
2026 | 16 |  |
2027 | 15 |  |
2028 | 15 |  |
2029 | 14 |  |
2030 to 2034 | $ 61 |  |

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