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RETIREMENT BENEFITS - Actuarial Assumptions (Details)
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Pension plans      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 3.09% 2.81% 3.41%
Expected long-term return on plan assets 8.25% 8.25% 8.25%
Annual salary increase, net periodic costs 4.80% 4.80% 4.73%
Pension plans | Discount rate – interest costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 2.55% 2.13% 2.99%
Pension plans | Discount rate – service costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 3.34% 3.18% 3.66%
Pension plans | Employee benefit obligations      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 5.25% 3.09%  
Annual salary increase 4.80% 4.80%  
Other postretirement benefit plans      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 2.90% 2.56% 3.24%
Expected long-term return on plan assets 7.21% 7.09% 7.25%
Annual salary increase, net periodic costs 4.80% 4.80% 4.73%
Other postretirement benefit plans | Discount rate – interest costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 2.32% 1.84% 2.80%
Other postretirement benefit plans | Discount rate – service costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 3.26% 3.07% 3.57%
Other postretirement benefit plans | Employee benefit obligations      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 5.18% 2.90%  
Annual salary increase 4.80% 4.80%  
Alabama Power | Pension plans      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 3.12% 2.85% 3.44%
Expected long-term return on plan assets 8.25% 8.25% 8.25%
Annual salary increase, net periodic costs 4.80% 4.80% 4.73%
Alabama Power | Pension plans | Discount rate – interest costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 2.58% 2.17% 3.01%
Alabama Power | Pension plans | Discount rate – service costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 3.36% 3.23% 3.69%
Alabama Power | Pension plans | Employee benefit obligations      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 5.26% 3.12%  
Annual salary increase 4.80% 4.80%  
Alabama Power | Other postretirement benefit plans      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 2.95% 2.63% 3.28%
Expected long-term return on plan assets 7.54% 7.18% 7.36%
Annual salary increase, net periodic costs 4.80% 4.80% 4.73%
Alabama Power | Other postretirement benefit plans | Discount rate – interest costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 2.38% 1.91% 2.84%
Alabama Power | Other postretirement benefit plans | Discount rate – service costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 3.30% 3.13% 3.61%
Alabama Power | Other postretirement benefit plans | Employee benefit obligations      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 5.20% 2.95%  
Annual salary increase 4.80% 4.80%  
Georgia Power | Pension plans      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 3.07% 2.79% 3.40%
Expected long-term return on plan assets 8.25% 8.25% 8.25%
Annual salary increase, net periodic costs 4.80% 4.80% 4.73%
Georgia Power | Pension plans | Discount rate – interest costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 2.51% 2.09% 2.96%
Georgia Power | Pension plans | Discount rate – service costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 3.37% 3.21% 3.67%
Georgia Power | Pension plans | Employee benefit obligations      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 5.25% 3.07%  
Annual salary increase 4.80% 4.80%  
Georgia Power | Other postretirement benefit plans      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 2.87% 2.52% 3.22%
Expected long-term return on plan assets 6.88% 6.84% 7.05%
Annual salary increase, net periodic costs 4.80% 4.80% 4.73%
Georgia Power | Other postretirement benefit plans | Discount rate – interest costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 2.30% 1.82% 2.79%
Georgia Power | Other postretirement benefit plans | Discount rate – service costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 3.27% 3.08% 3.57%
Georgia Power | Other postretirement benefit plans | Employee benefit obligations      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 5.17% 2.87%  
Annual salary increase 4.80% 4.80%  
Mississippi Power | Pension plans      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 3.07% 2.80% 3.41%
Expected long-term return on plan assets 8.25% 8.25% 8.25%
Annual salary increase, net periodic costs 4.80% 4.80% 4.73%
Mississippi Power | Pension plans | Discount rate – interest costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 2.54% 2.12% 2.99%
Mississippi Power | Pension plans | Discount rate – service costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 3.35% 3.20% 3.67%
Mississippi Power | Pension plans | Employee benefit obligations      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 5.25% 3.07%  
Annual salary increase 4.80% 4.80%  
Mississippi Power | Other postretirement benefit plans      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 2.88% 2.53% 3.22%
Expected long-term return on plan assets 7.22% 6.98% 7.07%
Annual salary increase, net periodic costs 4.80% 4.80% 4.73%
Mississippi Power | Other postretirement benefit plans | Discount rate – interest costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 2.27% 1.78% 2.76%
Mississippi Power | Other postretirement benefit plans | Discount rate – service costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 3.26% 3.06% 3.57%
Mississippi Power | Other postretirement benefit plans | Employee benefit obligations      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 5.17% 2.88%  
Annual salary increase 4.80% 4.80%  
Southern Power | Pension plans      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 3.21% 2.99% 3.52%
Expected long-term return on plan assets 8.25% 8.25% 8.25%
Annual salary increase, net periodic costs 4.80% 4.80% 4.73%
Southern Power | Pension plans | Discount rate – interest costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 2.79% 2.46% 3.18%
Southern Power | Pension plans | Discount rate – service costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 3.36% 3.22% 3.70%
Southern Power | Pension plans | Employee benefit obligations      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 5.31% 3.21%  
Annual salary increase 4.80% 4.80%  
Southern Power | Other postretirement benefit plans      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 3.07% 2.78% 3.39%
Expected long-term return on plan assets 0.00% 0.00% 0.00%
Annual salary increase, net periodic costs 4.80% 4.80% 4.73%
Southern Power | Other postretirement benefit plans | Discount rate – interest costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 2.55% 2.12% 2.97%
Southern Power | Other postretirement benefit plans | Discount rate – service costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 3.25% 3.05% 3.57%
Southern Power | Other postretirement benefit plans | Employee benefit obligations      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 5.24% 3.07%  
Annual salary increase 4.80% 4.80%  
Southern Company Gas | Pension plans      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 3.04% 2.75% 3.39%
Expected long-term return on plan assets 8.25% 8.25% 8.25%
Annual salary increase, net periodic costs 4.80% 4.80% 4.73%
Southern Company Gas | Pension plans | Discount rate – interest costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 2.53% 2.10% 2.99%
Southern Company Gas | Pension plans | Discount rate – service costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 3.21% 2.97% 3.53%
Southern Company Gas | Pension plans | Employee benefit obligations      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 5.24% 3.04%  
Annual salary increase 4.80% 4.80%  
Southern Company Gas | Other postretirement benefit plans      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 2.82% 2.46% 3.19%
Expected long-term return on plan assets 6.08% 6.54% 6.69%
Annual salary increase, net periodic costs 4.80% 4.80% 4.73%
Southern Company Gas | Other postretirement benefit plans | Discount rate – interest costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 2.17% 1.64% 2.71%
Southern Company Gas | Other postretirement benefit plans | Discount rate – service costs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, net periodic benefit costs 3.22% 3.01% 3.52%
Southern Company Gas | Other postretirement benefit plans | Employee benefit obligations      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate – benefit obligations 5.16% 2.82%  
Annual salary increase 4.80% 4.80%