FINANCING - Narrative (Details) $ in Millions	Sep. 30, 2020 USD ($)
Debt Instrument [Line Items]
Line of credit expiring in 2023	$ 125
Variable rate pollution control revenue bonds outstanding	1,400
MISSISSIPPI POWER CO
Debt Instrument [Line Items]
Line of credit expiring in 2023	125
Variable rate pollution control revenue bonds outstanding	34
ALABAMA POWER CO
Debt Instrument [Line Items]
Line of credit expiring in 2023	0
Variable rate pollution control revenue bonds outstanding	854
GEORGIA POWER CO
Debt Instrument [Line Items]
Line of credit expiring in 2023	0
Variable rate pollution control revenue bonds outstanding	550
Fixed rate pollution control revenue bonds outstanding	$ 257