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RETIREMENT BENEFITS - Actuarial Assumptions (Details) | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Pension plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 2.81% | 3.41% | 4.49%
Expected long-term return on plan assets | 8.25% | 8.25% | 7.75%
Annual salary increase, net periodic costs | 4.80% | 4.73% | 4.34%
Pension plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 2.13% | 2.99% | 4.12%
Pension plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 3.18% | 3.66% | 4.70%
Pension plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 3.09% | 2.81% |
Annual salary increase | 4.80% | 4.80% |
Other postretirement benefit plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 2.56% | 3.24% | 4.37%
Expected long-term return on plan assets | 7.09% | 7.25% | 6.86%
Annual salary increase, net periodic costs | 4.80% | 4.73% | 4.34%
Other postretirement benefit plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 1.84% | 2.80% | 3.98%
Other postretirement benefit plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 3.07% | 3.57% | 4.63%
Other postretirement benefit plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 2.90% | 2.56% |
Annual salary increase | 4.80% | 4.80% |
Alabama Power | Pension plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 2.85% | 3.44% | 4.51%
Expected long-term return on plan assets | 8.25% | 8.25% | 7.75%
Annual salary increase, net periodic costs | 4.80% | 4.73% | 4.46%
Alabama Power | Pension plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 2.17% | 3.01% | 4.14%
Alabama Power | Pension plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 3.23% | 3.69% | 4.73%
Alabama Power | Pension plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 3.12% | 2.85% |
Annual salary increase | 4.80% | 4.80% |
Alabama Power | Other postretirement benefit plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 2.63% | 3.28% | 4.40%
Expected long-term return on plan assets | 7.18% | 7.36% | 6.76%
Annual salary increase, net periodic costs | 4.80% | 4.73% | 4.46%
Alabama Power | Other postretirement benefit plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 1.91% | 2.84% | 4.01%
Alabama Power | Other postretirement benefit plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 3.13% | 3.61% | 4.67%
Alabama Power | Other postretirement benefit plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 2.95% | 2.63% |
Annual salary increase | 4.80% | 4.80% |
Georgia Power | Pension plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 2.79% | 3.40% | 4.48%
Expected long-term return on plan assets | 8.25% | 8.25% | 7.75%
Annual salary increase, net periodic costs | 4.80% | 4.73% | 4.46%
Georgia Power | Pension plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 2.09% | 2.96% | 4.10%
Georgia Power | Pension plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 3.21% | 3.67% | 4.72%
Georgia Power | Pension plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 3.07% | 2.79% |
Annual salary increase | 4.80% | 4.80% |
Georgia Power | Other postretirement benefit plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 2.52% | 3.22% | 4.36%
Expected long-term return on plan assets | 6.84% | 7.05% | 6.85%
Annual salary increase, net periodic costs | 4.80% | 4.73% | 4.46%
Georgia Power | Other postretirement benefit plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 1.82% | 2.79% | 3.97%
Georgia Power | Other postretirement benefit plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 3.08% | 3.57% | 4.64%
Georgia Power | Other postretirement benefit plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 2.87% | 2.52% |
Annual salary increase | 4.80% | 4.80% |
Mississippi Power | Pension plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 2.80% | 3.41% | 4.49%
Expected long-term return on plan assets | 8.25% | 8.25% | 7.75%
Annual salary increase, net periodic costs | 4.80% | 4.73% | 4.46%
Mississippi Power | Pension plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 2.12% | 2.99% | 4.12%
Mississippi Power | Pension plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 3.20% | 3.67% | 4.73%
Mississippi Power | Pension plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 3.07% | 2.80% |
Annual salary increase | 4.80% | 4.80% |
Mississippi Power | Other postretirement benefit plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 2.53% | 3.22% | 4.35%
Expected long-term return on plan assets | 6.98% | 7.07% | 6.79%
Annual salary increase, net periodic costs | 4.80% | 4.73% | 4.46%
Mississippi Power | Other postretirement benefit plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 1.78% | 2.76% | 3.95%
Mississippi Power | Other postretirement benefit plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 3.06% | 3.57% | 4.64%
Mississippi Power | Other postretirement benefit plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 2.88% | 2.53% |
Annual salary increase | 4.80% | 4.80% |
Southern Power | Pension plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 2.99% | 3.52% | 4.65%
Expected long-term return on plan assets | 8.25% | 8.25% | 7.75%
Annual salary increase, net periodic costs | 4.80% | 4.73% | 4.46%
Southern Power | Pension plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 2.46% | 3.18% | 4.35%
Southern Power | Pension plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 3.22% | 3.70% | 4.75%
Southern Power | Pension plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 3.21% | 2.99% |
Annual salary increase | 4.80% | 4.80% |
Southern Power | Other postretirement benefit plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 2.78% | 3.39% | 4.50%
Expected long-term return on plan assets | 0.00% | 0.00% | 0.00%
Annual salary increase, net periodic costs | 4.80% | 4.73% | 4.46%
Southern Power | Other postretirement benefit plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 2.12% | 2.97% | 4.14%
Southern Power | Other postretirement benefit plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 3.05% | 3.57% | 4.65%
Southern Power | Other postretirement benefit plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 3.07% | 2.78% |
Annual salary increase | 4.80% | 4.80% |
Southern Company Gas | Pension plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 2.75% | 3.39% | 4.47%
Expected long-term return on plan assets | 8.25% | 8.25% | 7.75%
Annual salary increase, net periodic costs | 4.80% | 4.73% | 3.07%
Southern Company Gas | Pension plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 2.10% | 2.99% | 4.11%
Southern Company Gas | Pension plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 2.97% | 3.53% | 4.57%
Southern Company Gas | Pension plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 3.04% | 2.75% |
Annual salary increase | 4.80% | 4.80% |
Southern Company Gas | Other postretirement benefit plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 2.46% | 3.19% | 4.32%
Expected long-term return on plan assets | 6.54% | 6.69% | 6.49%
Annual salary increase, net periodic costs | 4.80% | 4.73% | 3.07%
Southern Company Gas | Other postretirement benefit plans | Discount rate – interest costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 1.64% | 2.71% | 3.91%
Southern Company Gas | Other postretirement benefit plans | Discount rate – service costs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate, net periodic benefit costs | 3.01% | 3.52% | 4.56%
Southern Company Gas | Other postretirement benefit plans | Employee benefit obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate – benefit obligations | 2.82% | 2.46% |
Annual salary increase | 4.80% | 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 -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(2) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 + Details
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