Leases - Lease Income (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	$ 2	$ 7
Lease income - operating leases	64	216
Variable lease income	141	324
Total lease income	207	547
ALABAMA POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0
Lease income - operating leases	6	19
Variable lease income	0	0
Total lease income	6	19
GEORGIA POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0
Lease income - operating leases	18	57
Variable lease income	0	0
Total lease income	18	57
MISSISSIPPI POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	2	7
Lease income - operating leases	0	0
Variable lease income	0	0
Total lease income	2	7
SOUTHERN POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0
Lease income - operating leases	31	111
Variable lease income	151	349
Total lease income	182	460
SOUTHERN Co GAS
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0
Lease income - operating leases	9	26
Variable lease income	0	0
Total lease income	$ 9	$ 26