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v3.25.3

Retirement Benefits (Tables) | 9 Months Ended
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Sep. 30, 2025
Retirement Benefits [Abstract] |
Schedule of Pension Plans and Postretirement Plans | Components of the net periodic benefit costs for the three and nine months ended September 30, 2025 and 2024 are presented in the following tables.
| Southern Company |  | Alabama Power |  | Georgia Power |  | Mississippi Power |  | Southern Power |  | Southern Company Gas
| (in millions)
Three Months Ended September 30, 2025 |  |  |  |  |  |  |  |  |  |
Pension Plans |  |  |  |  |  |  |  |  |  |  |
Service cost | $ | 66 |  |  | $ | 15 |  |  | $ | 16 |  |  | $ | 3 |  |  | $ | 1 |  |  | $ | 7 |
Interest cost | 166 |  |  | 39 |  |  | 49 |  |  | 7 |  |  | 2 |  |  | 11 |
Expected return on plan assets | (320) |  |  | (78) |  |  | (100) |  |  | (15) |  |  | (4) |  |  | (22) |
Amortization: |  |  |  |  |  |  |  |  |  |  |
Prior service costs | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | (1) |
Regulatory asset | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 4 |
Net loss | 9 |  |  | 2 |  |  | 5 |  |  | 2 |  |  | 1 |  |  | — |
Net periodic pension income | $ | (79) |  |  | $ | (22) |  |  | $ | (30) |  |  | $ | (3) |  |  | $ | — |  |  | $ | (1) |
Postretirement Benefits |  |  |  |  |  |  |  |  |  |  |
Service cost | $ | 4 |  |  | $ | 1 |  |  | $ | 1 |  |  | $ | — |  |  | $ | — |  |  | $ | — |
Interest cost | 17 |  |  | 5 |  |  | 6 |  |  | 1 |  |  | — |  |  | 2 |
Expected return on plan assets | (23) |  |  | (8) |  |  | (9) |  |  | (1) |  |  | — |  |  | (2) |
Amortization: |  |  |  |  |  |  |  |  |  |  |
Prior service costs | 1 |  |  | — |  |  | 1 |  |  | — |  |  | — |  |  | — |
Regulatory asset | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 1 |
Net gain | (4) |  |  | (2) |  |  | — |  |  | — |  |  | — |  |  | (2) |
Net periodic postretirement benefit income | $ | (5) |  |  | $ | (4) |  |  | $ | (1) |  |  | $ | — |  |  | $ | — |  |  | $ | (1) |
Nine Months Ended September 30, 2025 |  |  |  |  |  |  |  |  |  |
Pension Plans
Service cost | $ | 198 |  |  | $ | 45 |  |  | $ | 47 |  |  | $ | 8 |  |  | $ | 4 |  |  | $ | 20 |
Interest cost | 498 |  |  | 116 |  |  | 147 |  |  | 22 |  |  | 7 |  |  | 33 |
Expected return on plan assets | (960) |  |  | (234) |  |  | (298) |  |  | (44) |  |  | (12) |  |  | (65) |
Amortization: |  |  |  |  |  |  |  |  |  |  |
Prior service costs | — |  |  | — |  |  | 1 |  |  | — |  |  | — |  |  | (2) |
Regulatory asset | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 11 |
Net (gain) loss | 28 |  |  | 8 |  |  | 12 |  |  | 3 |  |  | — |  |  | (1) |
Net periodic pension income | $ | (236) |  |  | $ | (65) |  |  | $ | (91) |  |  | $ | (11) |  |  | $ | (1) |  |  | $ | (4) |
Postretirement Benefits
Service cost | $ | 10 |  |  | $ | 3 |  |  | $ | 3 |  |  | $ | — |  |  | $ | — |  |  | $ | 1 |
Interest cost | 52 |  |  | 13 |  |  | 19 |  |  | 2 |  |  | — |  |  | 6 |
Expected return on plan assets | (68) |  |  | (26) |  |  | (25) |  |  | (1) |  |  | — |  |  | (7) |
Amortization: |  |  |  |  |  |  |  |  |  |  |
Prior service costs | 2 |  |  | — |  |  | 1 |  |  | — |  |  | — |  |  | — |
Regulatory asset | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 5 |
Net gain | (11) |  |  | (2) |  |  | (2) |  |  | — |  |  | — |  |  | (6) |
Net periodic postretirement benefit cost (income) | $ | (15) |  |  | $ | (12) |  |  | $ | (4) |  |  | $ | 1 |  |  | $ | — |  |  | $ | (1) |
| Southern Company |  | Alabama Power |  | Georgia Power |  | Mississippi Power |  | Southern Power |  | Southern Company Gas
| (in millions)
Three Months Ended September 30, 2024 |  |  |  |  |  |  |  |  |  |
Pension Plans
Service cost | $ | 73 |  |  | $ | 17 |  |  | $ | 18 |  |  | $ | 3 |  |  | $ | 2 |  |  | $ | 7 |
Interest cost | 159 |  |  | 37 |  |  | 47 |  |  | 7 |  |  | 2 |  |  | 11 |
Expected return on plan assets | (316) |  |  | (77) |  |  | (99) |  |  | (14) |  |  | (4) |  |  | (21) |
Amortization: |  |  |  |  |  |  |  |  |  |  |
Prior service costs | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | (1) |
Regulatory asset | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 4 |
Net (gain) loss | 14 |  |  | 4 |  |  | 6 |  |  | — |  |  | (1) |  |  | — |
Net periodic pension income | $ | (70) |  |  | $ | (19) |  |  | $ | (28) |  |  | $ | (4) |  |  | $ | (1) |  |  | $ | — |
Postretirement Benefits |  |  |  |  |  |  |  |  |  |  |
Service cost | $ | 4 |  |  | $ | 1 |  |  | $ | 1 |  |  | $ | — |  |  | $ | — |  |  | $ | — |
Interest cost | 16 |  |  | 4 |  |  | 6 |  |  | 1 |  |  | — |  |  | 2 |
Expected return on plan assets | (22) |  |  | (9) |  |  | (8) |  |  | (1) |  |  | — |  |  | (2) |
Amortization: |  |  |  |  |  |  |  |  |  |  |
Prior service costs | 1 |  |  | — |  |  | 1 |  |  | — |  |  | — |  |  | — |
Regulatory asset | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 2 |
Net (gain) loss | (4) |  |  | — |  |  | (3) |  |  | 1 |  |  | — |  |  | (1) |
Net periodic postretirement benefit cost (income) | $ | (5) |  |  | $ | (4) |  |  | $ | (3) |  |  | $ | 1 |  |  | $ | — |  |  | $ | 1 |
Nine Months Ended September 30, 2024 |  |  |  |  |  |  |  |  |  |
Pension Plans
Service cost | $ | 219 |  |  | $ | 51 |  |  | $ | 53 |  |  | $ | 9 |  |  | $ | 5 |  |  | $ | 21 |
Interest cost | 476 |  |  | 111 |  |  | 143 |  |  | 21 |  |  | 6 |  |  | 32 |
Expected return on plan assets | (947) |  |  | (230) |  |  | (296) |  |  | (43) |  |  | (12) |  |  | (64) |
Amortization: |  |  |  |  |  |  |  |  |  |  |
Prior service costs | — |  |  | — |  |  | 1 |  |  | — |  |  | — |  |  | (2) |
Regulatory asset | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 11 |
Net loss | 41 |  |  | 12 |  |  | 15 |  |  | 2 |  |  | — |  |  | — |
Net periodic pension income | $ | (211) |  |  | $ | (56) |  |  | $ | (84) |  |  | $ | (11) |  |  | $ | (1) |  |  | $ | (2) |
Postretirement Benefits
Service cost | $ | 11 |  |  | $ | 3 |  |  | $ | 3 |  |  | $ | — |  |  | $ | — |  |  | $ | 1 |
Interest cost | 49 |  |  | 12 |  |  | 17 |  |  | 2 |  |  | — |  |  | 6 |
Expected return on plan assets | (66) |  |  | (26) |  |  | (24) |  |  | (1) |  |  | — |  |  | (6) |
Amortization: |  |  |  |  |  |  |  |  |  |  |
Prior service costs | 2 |  |  | — |  |  | 1 |  |  | — |  |  | — |  |  | — |
Regulatory asset | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 5 |
Net gain | (12) |  |  | (2) |  |  | (4) |  |  | — |  |  | — |  |  | (4) |
Net periodic postretirement benefit cost (income) | $ | (16) |  |  | $ | (13) |  |  | $ | (7) |  |  | $ | 1 |  |  | $ | — |  |  | $ | 2 |

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- Definition Tabular disclosure of the components of net benefit costs for pension plans and/or other employee benefit plans including service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) recognized due to settlements or curtailments. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (q) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 715 -SubTopic 20 -Subparagraph (h) -Name Accounting Standards Codification -Paragraph 1 -Section 50 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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