RETIREMENT BENEFITS - Actuarial Assumptions (Details)	12 Months Ended
	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%