LEASES - Other Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 308	$ 310	$ 323
Operating cash flows from finance leases	9	9	10
Financing cash flows from finance leases	17	22	32
ROU assets obtained in exchange for new operating lease obligations	64	227	118
ROU assets obtained in exchange for new finance lease obligations	$ 3	$ 10	35
Weighted-average remaining lease term in years:
Operating leases	15 years 10 months 24 days	14 years 6 months
Finance leases	18 years	18 years 2 months 12 days
Weighted-average discount rate:
Operating leases	4.41%	4.44%
Finance leases	4.82%	4.79%
Alabama Power
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 58	$ 55	54
Operating cash flows from finance leases	0	0	0
Financing cash flows from finance leases	1	1	1
ROU assets obtained in exchange for new operating lease obligations	3	63	7
ROU assets obtained in exchange for new finance lease obligations	$ 0	$ 2	2
Weighted-average remaining lease term in years:
Operating leases	9 years 1 month 6 days	7 years 9 months 18 days
Finance leases	8 years 8 months 12 days	9 years 8 months 12 days
Weighted-average discount rate:
Operating leases	4.37%	4.14%
Finance leases	3.09%	3.20%
Georgia Power
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 211	$ 215	210
Operating cash flows from finance leases	17	18	19
Financing cash flows from finance leases	9	11	13
ROU assets obtained in exchange for new operating lease obligations	9	32	21
ROU assets obtained in exchange for new finance lease obligations	$ 0	$ 0	24
Weighted-average remaining lease term in years:
Operating leases	8 years 8 months 12 days	9 years 4 months 24 days
Finance leases	8 years 6 months	9 years 6 months
Weighted-average discount rate:
Operating leases	4.45%	4.37%
Finance leases	10.81%	10.81%
Mississippi Power
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 2	$ 3	3
Operating cash flows from finance leases	1	0	0
Financing cash flows from finance leases	1	0	0
ROU assets obtained in exchange for new operating lease obligations	0	0	0
ROU assets obtained in exchange for new finance lease obligations	$ 0	$ 0	0
Weighted-average remaining lease term in years:
Operating leases	6 years 1 month 6 days	6 years 6 months
Finance leases	13 years 10 months 24 days	14 years 10 months 24 days
Weighted-average discount rate:
Operating leases	2.74%	3.26%
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	$ 28	$ 28	27
Operating cash flows from finance leases	0	0	0
Financing cash flows from finance leases	0	0	0
ROU assets obtained in exchange for new operating lease obligations	72	51	2
ROU assets obtained in exchange for new finance lease obligations	$ 0	$ 0	0
Weighted-average remaining lease term in years:
Operating leases	32 years 9 months 18 days	32 years 1 month 6 days
Weighted-average discount rate:
Operating leases	5.20%	5.45%
Southern Company Gas
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 19	$ 18	18
Operating cash flows from finance leases	0	0	0
Financing cash flows from finance leases	0	0	0
ROU assets obtained in exchange for new operating lease obligations	7	4	19
ROU assets obtained in exchange for new finance lease obligations	$ 0	$ 0	$ 0
Weighted-average remaining lease term in years:
Operating leases	10 years 6 months	9 years 9 months 18 days
Weighted-average discount rate:
Operating leases	3.61%	3.67%