Revenue from Contracts with Customers and Lease Income - Schedule of Lease Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	$ 4	$ 3	$ 7	$ 6
Lease income - operating leases	56	47	112	97
Variable lease income	128	126	212	200
Total lease income	188	176	331	303
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	6	41	13
Variable lease income	(1)	0	0	0
Total lease income	20	6	41	13
GEORGIA POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0	0	0
Lease income - operating leases	10	15	21	30
Variable lease income	0	0	0	0
Total lease income	10	15	21	30
MISSISSIPPI POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	4	3	7	5
Lease income - operating leases	0	0	1	0
Variable lease income	0	0	0	0
Total lease income	4	3	8	5
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	42	45
Variable lease income	138	136	228	215
Total lease income	159	157	270	260
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	17	17
Variable lease income	0	0	0	0
Total lease income	$ 9	$ 9	$ 17	$ 17