Leases - Lease Income (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	$ 2
Lease income - operating leases	71
Variable lease income	66
Total lease income	139
GEORGIA POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0
Lease income - operating leases	19
Variable lease income	0
Total lease income	19
MISSISSIPPI POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	2
Lease income - operating leases	0
Variable lease income	0
Total lease income	2
SOUTHERN POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0
Lease income - operating leases	41
Variable lease income	72
Total lease income	113
SOUTHERN Co GAS
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0
Lease income - operating leases	9
Variable lease income	0
Total lease income	$ 9