Revenue from Contracts with Customers and Lease Income - Schedule of Lease Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	$ 5	$ 6
Lease income - operating leases	34	33
Variable lease income	79	81
Total lease income	118	120
ALABAMA POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0
Lease income - operating leases	3	2
Variable lease income	0	0
Total lease income	3	2
GEORGIA POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0
Lease income - operating leases	7	7
Variable lease income	0	0
Total lease income	7	7
MISSISSIPPI POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	3	4
Lease income - operating leases	1	1
Variable lease income	0	0
Total lease income	4	5
SOUTHERN POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	2	2
Lease income - operating leases	37	37
Variable lease income	87	89
Total lease income	126	128
SOUTHERN Co GAS
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0
Lease income - operating leases	9	9
Variable lease income	0	0
Total lease income	$ 9	$ 9