Leases - Other Information (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($)
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 129
Operating cash flows from finance leases	2
Financing cash flows from finance leases	16
ROU assets obtained in exchange for new operating lease obligations	55
ROU assets obtained in exchange for new finance lease obligations	$ 33
Weighted-average remaining lease term in years:
Operating leases	14 years
Finance leases	18 years 3 months 18 days
Weighted-average discount rate:
Operating leases	4.53%
Finance leases	5.05%
ALABAMA POWER CO
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 20
Operating cash flows from finance leases	0
Financing cash flows from finance leases	0
ROU assets obtained in exchange for new operating lease obligations	5
ROU assets obtained in exchange for new finance lease obligations	$ 1
Weighted-average remaining lease term in years:
Operating leases	3 years 7 months 6 days
Finance leases	12 years 9 months 18 days
Weighted-average discount rate:
Operating leases	3.33%
Finance leases	3.67%
GEORGIA POWER CO
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 75
Operating cash flows from finance leases	10
Financing cash flows from finance leases	3
ROU assets obtained in exchange for new operating lease obligations	13
ROU assets obtained in exchange for new finance lease obligations	$ 28
Weighted-average remaining lease term in years:
Operating leases	10 years 6 months
Finance leases	11 years
Weighted-average discount rate:
Operating leases	4.46%
Finance leases	10.69%
MISSISSIPPI POWER CO
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 1
Operating cash flows from finance leases	0
Financing cash flows from finance leases	0
ROU assets obtained in exchange for new operating lease obligations	0
ROU assets obtained in exchange for new finance lease obligations	$ 0
Weighted-average remaining lease term in years:
Operating leases	7 years
Weighted-average discount rate:
Operating leases	4.06%
SOUTHERN POWER CO
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 12
Operating cash flows from finance leases	0
Financing cash flows from finance leases	0
ROU assets obtained in exchange for new operating lease obligations	0
ROU assets obtained in exchange for new finance lease obligations	$ 0
Weighted-average remaining lease term in years:
Operating leases	33 years 6 months
Weighted-average discount rate:
Operating leases	5.68%
SOUTHERN Co GAS
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 9
Operating cash flows from finance leases	0
Financing cash flows from finance leases	0
ROU assets obtained in exchange for new operating lease obligations	13
ROU assets obtained in exchange for new finance lease obligations	$ 0
Weighted-average remaining lease term in years:
Operating leases	9 years 8 months 12 days
Weighted-average discount rate:
Operating leases	3.73%