Leases - Lease Income (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	$ 2	$ 5
Lease income - operating leases	67	139
Variable lease income	115	182
Total lease income	184	326
GEORGIA POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0
Lease income - operating leases	19	39
Variable lease income	0	0
Total lease income	19	39
MISSISSIPPI POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	2	5
Lease income - operating leases	0	0
Variable lease income	0	0
Total lease income	2	5
SOUTHERN POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0
Lease income - operating leases	39	80
Variable lease income	125	198
Total lease income	164	278
SOUTHERN Co GAS
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0
Lease income - operating leases	9	17
Variable lease income	0	0
Total lease income	$ 9	$ 17