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RETIREMENT BENEFITS - Actuarial Assumptions (Details) | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Pension plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.25% | 3.09% | 2.81%
Expected long-term return on plan assets | 8.40% | 8.25% | 8.25%
Annual salary increase, net periodic costs | 4.80% | 4.80% | 4.80%
Pension plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.13% | 2.55% | 2.13%
Pension plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.36% | 3.34% | 3.18%
Pension plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.07% | 5.25% |
Annual salary increase | 4.60% | 4.80% |
Other postretirement benefit plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.18% | 2.90% | 2.56%
Expected long-term return on plan assets | 7.67% | 7.21% | 7.09%
Annual salary increase, net periodic costs | 4.80% | 4.80% | 4.80%
Other postretirement benefit plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.08% | 2.32% | 1.84%
Other postretirement benefit plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.34% | 3.26% | 3.07%
Other postretirement benefit plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 4.99% | 5.18% |
Annual salary increase | 4.60% | 4.80% |
Alabama Power | Pension plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.26% | 3.12% | 2.85%
Expected long-term return on plan assets | 8.40% | 8.25% | 8.25%
Annual salary increase, net periodic costs | 4.80% | 4.80% | 4.80%
Alabama Power | Pension plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.14% | 2.58% | 2.17%
Alabama Power | Pension plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.38% | 3.36% | 3.23%
Alabama Power | Pension plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.08% | 5.26% |
Annual salary increase | 4.60% | 4.80% |
Alabama Power | Other postretirement benefit plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.20% | 2.95% | 2.63%
Expected long-term return on plan assets | 7.95% | 7.54% | 7.18%
Annual salary increase, net periodic costs | 4.80% | 4.80% | 4.80%
Alabama Power | Other postretirement benefit plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.09% | 2.38% | 1.91%
Alabama Power | Other postretirement benefit plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.35% | 3.30% | 3.13%
Alabama Power | Other postretirement benefit plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.01% | 5.20% |
Annual salary increase | 4.60% | 4.80% |
Georgia Power | Pension plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.25% | 3.07% | 2.79%
Expected long-term return on plan assets | 8.40% | 8.25% | 8.25%
Annual salary increase, net periodic costs | 4.80% | 4.80% | 4.80%
Georgia Power | Pension plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.12% | 2.51% | 2.09%
Georgia Power | Pension plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.38% | 3.37% | 3.21%
Georgia Power | Pension plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.06% | 5.25% |
Annual salary increase | 4.60% | 4.80% |
Georgia Power | Other postretirement benefit plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.17% | 2.87% | 2.52%
Expected long-term return on plan assets | 7.49% | 6.88% | 6.84%
Annual salary increase, net periodic costs | 4.80% | 4.80% | 4.80%
Georgia Power | Other postretirement benefit plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.07% | 2.30% | 1.82%
Georgia Power | Other postretirement benefit plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.34% | 3.27% | 3.08%
Georgia Power | Other postretirement benefit plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 4.98% | 5.17% |
Annual salary increase | 4.60% | 4.80% |
Mississippi Power | Pension plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.25% | 3.07% | 2.80%
Expected long-term return on plan assets | 8.40% | 8.25% | 8.25%
Annual salary increase, net periodic costs | 4.80% | 4.80% | 4.80%
Mississippi Power | Pension plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.12% | 2.54% | 2.12%
Mississippi Power | Pension plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.37% | 3.35% | 3.20%
Mississippi Power | Pension plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.06% | 5.25% |
Annual salary increase | 4.60% | 4.80% |
Mississippi Power | Other postretirement benefit plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.17% | 2.88% | 2.53%
Expected long-term return on plan assets | 7.43% | 7.22% | 6.98%
Annual salary increase, net periodic costs | 4.80% | 4.80% | 4.80%
Mississippi Power | Other postretirement benefit plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.08% | 2.27% | 1.78%
Mississippi Power | Other postretirement benefit plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.33% | 3.26% | 3.06%
Mississippi Power | Other postretirement benefit plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 4.98% | 5.17% |
Annual salary increase | 4.60% | 4.80% |
Southern Power | Pension plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.31% | 3.21% | 2.99%
Expected long-term return on plan assets | 8.40% | 8.25% | 8.25%
Annual salary increase, net periodic costs | 4.80% | 4.80% | 4.80%
Southern Power | Pension plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.19% | 2.79% | 2.46%
Southern Power | Pension plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.37% | 3.36% | 3.22%
Southern Power | Pension plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.14% | 5.31% |
Annual salary increase | 4.60% | 4.80% |
Southern Power | Other postretirement benefit plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.24% | 3.07% | 2.78%
Expected long-term return on plan assets | 0.00% | 0.00% | 0.00%
Annual salary increase, net periodic costs | 4.80% | 4.80% | 4.80%
Southern Power | Other postretirement benefit plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.12% | 2.55% | 2.12%
Southern Power | Other postretirement benefit plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.33% | 3.25% | 3.05%
Southern Power | Other postretirement benefit plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.06% | 5.24% |
Annual salary increase | 4.60% | 4.80% |
Southern Company Gas | Pension plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.24% | 3.04% | 2.75%
Expected long-term return on plan assets | 8.40% | 8.25% | 8.25%
Annual salary increase, net periodic costs | 4.80% | 4.80% | 4.80%
Southern Company Gas | Pension plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.12% | 2.53% | 2.10%
Southern Company Gas | Pension plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.31% | 3.21% | 2.97%
Southern Company Gas | Pension plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.05% | 5.24% |
Annual salary increase | 4.60% | 4.80% |
Southern Company Gas | Other postretirement benefit plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 5.16% | 2.82% | 2.46%
Expected long-term return on plan assets | 6.59% | 6.08% | 6.54%
Annual salary increase, net periodic costs | 4.80% | 4.80% | 4.80%
Southern Company Gas | Other postretirement benefit plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.07% | 2.17% | 1.64%
Southern Company Gas | Other postretirement benefit plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 5.33% | 3.22% | 3.01%
Southern Company Gas | Other postretirement benefit plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 4.98% | 5.16% |
Annual salary increase | 4.60% | 4.80% |

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- Definition Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k)(2) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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