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Retirement Benefits (Details) - USD ($) | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2024 | Jun. 30, 2023 | Jun. 30, 2024 | Jun. 30, 2023
Pension Plans |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined benefit plan, expected future employer contributions, remainder of fiscal year | $ 0 |  | $ 0 |
Pension Plans and Postretirement Plans |  |  |  |
Service cost | 73,000,000 | $ 69,000,000 | 146,000,000 | $ 138,000,000
Interest cost | 158,000,000 | 157,000,000 | 317,000,000 | 313,000,000
Expected return on plan assets | (315,000,000) | (308,000,000) | (631,000,000) | (615,000,000)
Amortization: |  |  |  |
Prior service costs | 0 | 0 | 0 | 0
Regulatory asset | 0 | 0 | 0 | 0
Net loss | 13,000,000 | 8,000,000 | 27,000,000 | 16,000,000
Net periodic pension income | (71,000,000) | (74,000,000) | (141,000,000) | (148,000,000)
Pension Plans | ALABAMA POWER CO |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |
Service cost | 17,000,000 | 16,000,000 | 34,000,000 | 32,000,000
Interest cost | 37,000,000 | 36,000,000 | 74,000,000 | 72,000,000
Expected return on plan assets | (76,000,000) | (74,000,000) | (153,000,000) | (148,000,000)
Amortization: |  |  |  |
Prior service costs | 0 | 0 | 0 | 0
Regulatory asset | 0 | 0 | 0 | 0
Net loss | 4,000,000 | 3,000,000 | 8,000,000 | 5,000,000
Net periodic pension income | (18,000,000) | (19,000,000) | (37,000,000) | (39,000,000)
Pension Plans | GEORGIA POWER CO |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |
Service cost | 17,000,000 | 17,000,000 | 35,000,000 | 34,000,000
Interest cost | 48,000,000 | 47,000,000 | 96,000,000 | 95,000,000
Expected return on plan assets | (98,000,000) | (96,000,000) | (197,000,000) | (192,000,000)
Amortization: |  |  |  |
Prior service costs | 1,000,000 | 1,000,000 | 1,000,000 | 1,000,000
Regulatory asset | 0 | 0 | 0 | 0
Net loss | 4,000,000 | 3,000,000 | 9,000,000 | 6,000,000
Net periodic pension income | (28,000,000) | (28,000,000) | (56,000,000) | (56,000,000)
Pension Plans | MISSISSIPPI POWER CO |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |
Service cost | 3,000,000 | 3,000,000 | 6,000,000 | 6,000,000
Interest cost | 7,000,000 | 7,000,000 | 14,000,000 | 14,000,000
Expected return on plan assets | (15,000,000) | (14,000,000) | (29,000,000) | (28,000,000)
Amortization: |  |  |  |
Prior service costs | 0 | 0 | 0 | 0
Regulatory asset | 0 | 0 | 0 | 0
Net loss | 2,000,000 | 0 | 2,000,000 | 0
Net periodic pension income | (3,000,000) | (4,000,000) | (7,000,000) | (8,000,000)
Pension Plans | SOUTHERN POWER CO |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |
Service cost | 1,000,000 | 1,000,000 | 3,000,000 | 3,000,000
Interest cost | 2,000,000 | 2,000,000 | 4,000,000 | 4,000,000
Expected return on plan assets | (4,000,000) | (4,000,000) | (8,000,000) | (8,000,000)
Amortization: |  |  |  |
Prior service costs | 0 | 0 | 0 | 0
Regulatory asset | 0 | 0 | 0 | 0
Net loss | 1,000,000 | 0 | 1,000,000 | 0
Net periodic pension income | 0 | (1,000,000) | 0 | (1,000,000)
Pension Plans | SOUTHERN Co GAS |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |
Service cost | 7,000,000 | 6,000,000 | 14,000,000 | 12,000,000
Interest cost | 11,000,000 | 11,000,000 | 21,000,000 | 21,000,000
Expected return on plan assets | (21,000,000) | (22,000,000) | (43,000,000) | (44,000,000)
Amortization: |  |  |  |
Prior service costs | (1,000,000) | (1,000,000) | (1,000,000) | (1,000,000)
Regulatory asset | 4,000,000 | 4,000,000 | 8,000,000 | 8,000,000
Net loss | 0 | (1,000,000) | 0 | (2,000,000)
Net periodic pension income | 0 | (3,000,000) | (1,000,000) | (6,000,000)
Postretirement Benefits |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |
Service cost | 3,000,000 | 3,000,000 | 7,000,000 | 7,000,000
Interest cost | 17,000,000 | 17,000,000 | 33,000,000 | 35,000,000
Expected return on plan assets | (22,000,000) | (20,000,000) | (44,000,000) | (41,000,000)
Amortization: |  |  |  |
Prior service costs |  | 1,000,000 | 1,000,000 | 1,000,000
Regulatory asset | 0 | 0 | 0 | 0
Net loss | (4,000,000) | (3,000,000) | (8,000,000) | (6,000,000)
Net periodic pension income | (6,000,000) | (2,000,000) | (11,000,000) | (4,000,000)
Postretirement Benefits | ALABAMA POWER CO |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |
Service cost | 1,000,000 | 1,000,000 | 2,000,000 | 2,000,000
Interest cost | 4,000,000 | 4,000,000 | 8,000,000 | 8,000,000
Expected return on plan assets | (8,000,000) | (9,000,000) | (17,000,000) | (17,000,000)
Amortization: |  |  |  |
Prior service costs |  | 0 | 0 | 0
Regulatory asset | 0 | 0 | 0 | 0
Net loss | (2,000,000) | 0 | (2,000,000) | (1,000,000)
Net periodic pension income | (5,000,000) | (4,000,000) | (9,000,000) | (8,000,000)
Postretirement Benefits | GEORGIA POWER CO |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |
Service cost | 1,000,000 | 1,000,000 | 2,000,000 | 2,000,000
Interest cost | 5,000,000 | 7,000,000 | 11,000,000 | 13,000,000
Expected return on plan assets | (8,000,000) | (8,000,000) | (16,000,000) | (15,000,000)
Amortization: |  |  |  |
Prior service costs |  | 0 | 0 | 0
Regulatory asset | 0 | 0 | 0 | 0
Net loss | 0 | (1,000,000) | (1,000,000) | (2,000,000)
Net periodic pension income | (2,000,000) | (1,000,000) | (4,000,000) | (2,000,000)
Postretirement Benefits | MISSISSIPPI POWER CO |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |
Service cost | 0 | 0 | 0 | 0
Interest cost | 0 | 1,000,000 | 1,000,000 | 2,000,000
Expected return on plan assets | 0 | 0 | 0 | (1,000,000)
Amortization: |  |  |  |
Prior service costs |  | 0 | 0 | 0
Regulatory asset | 0 | 0 | 0 | 0
Net loss | 0 | 0 | (1,000,000) | 0
Net periodic pension income | 0 | 1,000,000 | 0 | 1,000,000
Postretirement Benefits | SOUTHERN POWER CO |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |
Service cost | 0 | 0 | 0 | 0
Interest cost | 0 | 0 | 0 | 0
Expected return on plan assets | 0 | 0 | 0 | 0
Amortization: |  |  |  |
Prior service costs |  | 0 | 0 | 0
Regulatory asset | 0 | 0 | 0 | 0
Net loss | 0 | 0 | 0 | 0
Net periodic pension income | 0 | 0 | 0 | 0
Postretirement Benefits | SOUTHERN Co GAS |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |
Service cost | 0 | 0 | 0 | 0
Interest cost | 2,000,000 | 2,000,000 | 4,000,000 | 4,000,000
Expected return on plan assets | (2,000,000) | (2,000,000) | (4,000,000) | (3,000,000)
Amortization: |  |  |  |
Prior service costs |  | 0 | 0 | 0
Regulatory asset | 2,000,000 | 2,000,000 | 3,000,000 | 3,000,000
Net loss | (1,000,000) | (1,000,000) | (3,000,000) | (2,000,000)
Net periodic pension income | $ 1,000,000 | $ 1,000,000 | $ 0 | $ 2,000,000

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