LEASES - Other Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 253	$ 303	$ 308
Operating cash flows from finance leases	15	11	9
Financing cash flows from finance leases	18	16	17
ROU assets obtained under operating leases	100	56	64
Reassessment of ROU assets under operating leases		16
ROU assets obtained under finance leases	$ 3	$ 118	3
Weighted-average remaining lease term in years:
Operating leases	17 years 2 months 12 days	17 years 3 months 18 days
Finance leases	16 years 8 months 12 days	17 years 4 months 24 days
Weighted-average discount rate:
Operating leases	4.68%	4.51%
Finance leases	4.85%	4.87%
Alabama Power
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 17	$ 58	58
Operating cash flows from finance leases	0	0	0
Financing cash flows from finance leases	2	1	1
ROU assets obtained under operating leases	30	10	3
Reassessment of ROU assets under operating leases		0
ROU assets obtained under finance leases	$ 3	$ 2	0
Weighted-average remaining lease term in years:
Operating leases	11 years 1 month 6 days	13 years
Finance leases	4 years 3 months 18 days	6 years 4 months 24 days
Weighted-average discount rate:
Operating leases	5.02%	4.87%
Finance leases	3.93%	3.00%
Georgia Power
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 199	$ 206	211
Operating cash flows from finance leases	22	20	17
Financing cash flows from finance leases	16	10	9
ROU assets obtained under operating leases	26	17	9
Reassessment of ROU assets under operating leases		0
ROU assets obtained under finance leases	$ 18	$ 116	0
Weighted-average remaining lease term in years:
Operating leases	7 years 6 months	8 years 1 month 6 days
Finance leases	10 years 7 months 6 days	11 years 9 months 18 days
Weighted-average discount rate:
Operating leases	4.58%	4.52%
Finance leases	5.95%	8.06%
Mississippi Power
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 5	$ 5	2
Operating cash flows from finance leases	0	1	1
Financing cash flows from finance leases	1	1	1
ROU assets obtained under operating leases	1	9	0
Reassessment of ROU assets under operating leases		0
ROU assets obtained under finance leases	$ 0	$ 0	0
Weighted-average remaining lease term in years:
Operating leases	4 years 7 months 6 days	4 years 8 months 12 days
Finance leases	11 years 10 months 24 days	12 years 10 months 24 days
Weighted-average discount rate:
Operating leases	3.67%	3.49%
Finance leases	2.74%	2.74%
Southern Power
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 33	$ 30	28
Operating cash flows from finance leases	0	0	0
Financing cash flows from finance leases	0	0	0
ROU assets obtained under operating leases	7	0	72
Reassessment of ROU assets under operating leases		16
ROU assets obtained under finance leases	$ 0	$ 0	0
Weighted-average remaining lease term in years:
Operating leases	33 years 1 month 6 days	34 years
Weighted-average discount rate:
Operating leases	4.89%	4.86%
Southern Company Gas
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 12	$ 14	19
Operating cash flows from finance leases	0	0	0
Financing cash flows from finance leases	0	0	0
ROU assets obtained under operating leases	7	3	7
Reassessment of ROU assets under operating leases		0
ROU assets obtained under finance leases	$ 0	$ 0	$ 0
Weighted-average remaining lease term in years:
Operating leases	7 years	11 years
Weighted-average discount rate:
Operating leases	3.80%	3.79%