LEASES - Other Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 303	$ 308	$ 310
Operating cash flows from finance leases	11	9	9
Financing cash flows from finance leases	16	17	22
ROU assets obtained under operating leases	56	64	227
Reassessment of ROU assets under operating leases	16
ROU assets obtained under finance leases	$ 118	$ 3	10
Weighted-average remaining lease term in years:
Operating leases	17 years 3 months 18 days	15 years 10 months 24 days
Finance leases	17 years 4 months 24 days	18 years
Weighted-average discount rate:
Operating leases	4.51%	4.41%
Finance leases	4.87%	4.82%
Alabama Power
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 58	$ 58	55
Operating cash flows from finance leases	0	0	0
Financing cash flows from finance leases	1	1	1
ROU assets obtained under operating leases	10	3	63
Reassessment of ROU assets under operating leases	0
ROU assets obtained under finance leases	$ 2	$ 0	2
Weighted-average remaining lease term in years:
Operating leases	13 years	9 years 1 month 6 days
Finance leases	6 years 4 months 24 days	8 years 8 months 12 days
Weighted-average discount rate:
Operating leases	4.87%	4.37%
Finance leases	3.00%	3.09%
Georgia Power
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 206	$ 211	215
Operating cash flows from finance leases	20	17	18
Financing cash flows from finance leases	10	9	11
ROU assets obtained under operating leases	17	9	32
Reassessment of ROU assets under operating leases	0
ROU assets obtained under finance leases	$ 116	$ 0	0
Weighted-average remaining lease term in years:
Operating leases	8 years 1 month 6 days	8 years 8 months 12 days
Finance leases	11 years 9 months 18 days	8 years 6 months
Weighted-average discount rate:
Operating leases	4.52%	4.45%
Finance leases	8.06%	10.81%
Mississippi Power
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 5	$ 2	3
Operating cash flows from finance leases	1	1	0
Financing cash flows from finance leases	1	1	0
ROU assets obtained under operating leases	9	0	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 8 months 12 days	6 years 1 month 6 days
Finance leases	12 years 10 months 24 days	13 years 10 months 24 days
Weighted-average discount rate:
Operating leases	3.49%	2.74%
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	$ 30	$ 28	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	0	72	51
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	34 years	32 years 9 months 18 days
Weighted-average discount rate:
Operating leases	4.86%	5.20%
Southern Company Gas
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 14	$ 19	18
Operating cash flows from finance leases	0	0	0
Financing cash flows from finance leases	0	0	0
ROU assets obtained under operating leases	3	7	4
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	11 years	10 years 6 months
Weighted-average discount rate:
Operating leases	3.79%	3.61%