Revenue from Contracts with Customers and Lease Income - Schedule of Lease Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	$ 4	$ 3	$ 11	$ 8
Lease income - operating leases	56	50	168	148
Variable lease income	143	145	355	345
Total lease income	203	198	534	501
ALABAMA POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0	0	0
Lease income - operating leases	21	11	62	24
Variable lease income	0	0	0	0
Total lease income	21	11	62	24
GEORGIA POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0	0	0
Lease income - operating leases	11	14	31	44
Variable lease income	0	0	0	0
Total lease income	11	14	31	44
MISSISSIPPI POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	4	3	10	8
Lease income - operating leases	0	0	1	1
Variable lease income	0	0	0	0
Total lease income	4	3	11	9
SOUTHERN POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0	0	0
Lease income - operating leases	21	21	64	66
Variable lease income	151	153	379	368
Total lease income	172	174	443	434
SOUTHERN Co GAS
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0	0	0
Lease income - operating leases	9	9	26	26
Variable lease income	0	0	0	0
Total lease income	$ 9	$ 9	$ 26	$ 26