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Retirement Benefits (Details) - USD ($) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024 | Dec. 31, 2025
Pension Plans |  |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |  |
Service cost | $ 66,000,000 | $ 73,000,000 | $ 198,000,000 | $ 219,000,000 |
Interest cost | 166,000,000 | 159,000,000 | 498,000,000 | 476,000,000 |
Expected return on plan assets | (320,000,000) | (316,000,000) | (960,000,000) | (947,000,000) |
Amortization: |  |  |  |  |
Prior service costs | 0 | 0 | 0 | 0 |
Regulatory asset | 0 | 0 | 0 | 0 |
Net loss | 9,000,000 | 14,000,000 | 28,000,000 | 41,000,000 |
Net periodic pension income | (79,000,000) | (70,000,000) | (236,000,000) | (211,000,000) |
Pension Plans | Scenario, Forecast |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined benefit plan, expected future employer contributions, remainder of fiscal year |  |  |  |  | $ 0
Pension Plans | ALABAMA POWER CO |  |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |  |
Service cost | 15,000,000 | 17,000,000 | 45,000,000 | 51,000,000 |
Interest cost | 39,000,000 | 37,000,000 | 116,000,000 | 111,000,000 |
Expected return on plan assets | (78,000,000) | (77,000,000) | (234,000,000) | (230,000,000) |
Amortization: |  |  |  |  |
Prior service costs | 0 | 0 | 0 | 0 |
Regulatory asset | 0 | 0 | 0 | 0 |
Net loss | 2,000,000 | 4,000,000 | 8,000,000 | 12,000,000 |
Net periodic pension income | (22,000,000) | (19,000,000) | (65,000,000) | (56,000,000) |
Pension Plans | GEORGIA POWER CO |  |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |  |
Service cost | 16,000,000 | 18,000,000 | 47,000,000 | 53,000,000 |
Interest cost | 49,000,000 | 47,000,000 | 147,000,000 | 143,000,000 |
Expected return on plan assets | (100,000,000) | (99,000,000) | (298,000,000) | (296,000,000) |
Amortization: |  |  |  |  |
Prior service costs | 0 | 0 | 1,000,000 | 1,000,000 |
Regulatory asset | 0 | 0 | 0 | 0 |
Net loss | 5,000,000 | 6,000,000 | 12,000,000 | 15,000,000 |
Net periodic pension income | (30,000,000) | (28,000,000) | (91,000,000) | (84,000,000) |
Pension Plans | MISSISSIPPI POWER CO |  |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |  |
Service cost | 3,000,000 | 3,000,000 | 8,000,000 | 9,000,000 |
Interest cost | 7,000,000 | 7,000,000 | 22,000,000 | 21,000,000 |
Expected return on plan assets | (15,000,000) | (14,000,000) | (44,000,000) | (43,000,000) |
Amortization: |  |  |  |  |
Prior service costs | 0 | 0 | 0 | 0 |
Regulatory asset | 0 | 0 | 0 | 0 |
Net loss | 2,000,000 | 0 | 3,000,000 | 2,000,000 |
Net periodic pension income | (3,000,000) | (4,000,000) | (11,000,000) | (11,000,000) |
Pension Plans | SOUTHERN POWER CO |  |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |  |
Service cost | 1,000,000 | 2,000,000 | 4,000,000 | 5,000,000 |
Interest cost | 2,000,000 | 2,000,000 | 7,000,000 | 6,000,000 |
Expected return on plan assets | (4,000,000) | (4,000,000) | (12,000,000) | (12,000,000) |
Amortization: |  |  |  |  |
Prior service costs | 0 | 0 | 0 | 0 |
Regulatory asset | 0 | 0 | 0 | 0 |
Net loss | 1,000,000 | (1,000,000) | 0 | 0 |
Net periodic pension income | 0 | (1,000,000) | (1,000,000) | (1,000,000) |
Pension Plans | SOUTHERN Co GAS |  |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |  |
Service cost | 7,000,000 | 7,000,000 | 20,000,000 | 21,000,000 |
Interest cost | 11,000,000 | 11,000,000 | 33,000,000 | 32,000,000 |
Expected return on plan assets | (22,000,000) | (21,000,000) | (65,000,000) | (64,000,000) |
Amortization: |  |  |  |  |
Prior service costs | (1,000,000) | (1,000,000) | (2,000,000) | (2,000,000) |
Regulatory asset | 4,000,000 | 4,000,000 | 11,000,000 | 11,000,000 |
Net loss | 0 | 0 | (1,000,000) | 0 |
Net periodic pension income | (1,000,000) | 0 | (4,000,000) | (2,000,000) |
Postretirement Benefits |  |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |  |
Service cost | 4,000,000 | 4,000,000 | 10,000,000 | 11,000,000 |
Interest cost | 17,000,000 | 16,000,000 | 52,000,000 | 49,000,000 |
Expected return on plan assets | (23,000,000) | (22,000,000) | (68,000,000) | (66,000,000) |
Amortization: |  |  |  |  |
Prior service costs | 1,000,000 | 1,000,000 | 2,000,000 | 2,000,000 |
Regulatory asset | 0 | 0 | 0 | 0 |
Net loss | (4,000,000) | (4,000,000) | (11,000,000) | (12,000,000) |
Net periodic pension income | (5,000,000) | (5,000,000) | (15,000,000) | (16,000,000) |
Postretirement Benefits | ALABAMA POWER CO |  |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |  |
Service cost | 1,000,000 | 1,000,000 | 3,000,000 | 3,000,000 |
Interest cost | 5,000,000 | 4,000,000 | 13,000,000 | 12,000,000 |
Expected return on plan assets | (8,000,000) | (9,000,000) | (26,000,000) | (26,000,000) |
Amortization: |  |  |  |  |
Prior service costs | 0 | 0 | 0 | 0 |
Regulatory asset | 0 | 0 | 0 | 0 |
Net loss | (2,000,000) | 0 | (2,000,000) | (2,000,000) |
Net periodic pension income | (4,000,000) | (4,000,000) | (12,000,000) | (13,000,000) |
Postretirement Benefits | GEORGIA POWER CO |  |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |  |
Service cost | 1,000,000 | 1,000,000 | 3,000,000 | 3,000,000 |
Interest cost | 6,000,000 | 6,000,000 | 19,000,000 | 17,000,000 |
Expected return on plan assets | (9,000,000) | (8,000,000) | (25,000,000) | (24,000,000) |
Amortization: |  |  |  |  |
Prior service costs | 1,000,000 | 1,000,000 | 1,000,000 | 1,000,000 |
Regulatory asset | 0 | 0 | 0 | 0 |
Net loss | 0 | (3,000,000) | (2,000,000) | (4,000,000) |
Net periodic pension income | (1,000,000) | (3,000,000) | (4,000,000) | (7,000,000) |
Postretirement Benefits | MISSISSIPPI POWER CO |  |  |  |  |
Pension Plans and Postretirement Plans |  |  |  |  |
Service cost | 0 | 0 | 0 | 0 |
Interest cost | 1,000,000 | 1,000,000 | 2,000,000 | 2,000,000 |
Expected return on plan assets | (1,000,000) | (1,000,000) | (1,000,000) | (1,000,000) |
Amortization: |  |  |  |  |
Prior service costs | 0 | 0 | 0 | 0 |
Regulatory asset | 0 | 0 | 0 | 0 |
Net loss | 0 | 1,000,000 | 0 | 0 |
Net periodic pension income | 0 | 1,000,000 | 1,000,000 | 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 | 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 | 1,000,000 | 1,000,000 |
Interest cost | 2,000,000 | 2,000,000 | 6,000,000 | 6,000,000 |
Expected return on plan assets | (2,000,000) | (2,000,000) | (7,000,000) | (6,000,000) |
Amortization: |  |  |  |  |
Prior service costs | 0 | 0 | 0 | 0 |
Regulatory asset | 1,000,000 | 2,000,000 | 5,000,000 | 5,000,000 |
Net loss | (2,000,000) | (1,000,000) | (6,000,000) | (4,000,000) |
Net periodic pension income | $ (1,000,000) | $ 1,000,000 | $ (1,000,000) | $ 2,000,000 |

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