Revenue from Contracts with Customers and Lease Income - Schedule of Lease Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	$ 6	$ 5	$ 18	$ 18
Lease income - operating leases	38	38	104	108
Variable lease income	141	142	347	343
Total lease income	185	185	469	469
ALABAMA POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0	0	0
Lease income - operating leases	2	2	5	6
Variable lease income	0	0	1	0
Total lease income	2	2	6	6
GEORGIA POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0	0	0
Lease income - operating leases	7	13	22	28
Variable lease income	0	0	0	0
Total lease income	7	13	22	28
MISSISSIPPI POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	4	3	11	11
Lease income - operating leases	1	0	2	2
Variable lease income	0	0	0	0
Total lease income	5	3	13	13
SOUTHERN POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	2	2	7	7
Lease income - operating leases	37	20	111	63
Variable lease income	151	152	375	370
Total lease income	190	174	493	440
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	27	27
Variable lease income	0	0	0	0
Total lease income	$ 9	$ 9	$ 27	$ 27