LEASES - Lease Income (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	$ 9
Lease income - operating leases	273
Variable lease income	403
Total lease income	685
Alabama Power
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0
Lease income - operating leases	24
Variable lease income	0
Total lease income	24
Georgia Power
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0
Lease income - operating leases	71
Variable lease income	0
Total lease income	71
Mississippi Power
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	9
Lease income - operating leases	0
Variable lease income	0
Total lease income	9
Southern Power
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0
Lease income - operating leases	160
Variable lease income	434
Total lease income	594
Southern Company Gas
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0
Lease income - operating leases	35
Variable lease income	0
Total lease income	$ 35