INCOME TAXES (Details) - USD ($) $ in Billions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	13.90%	30.20%
GEORGIA POWER CO
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	12.30%	22.60%
MISSISSIPPI POWER CO
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	12.70%	16.30%
SOUTHERN POWER CO
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	11.30%	(13.60%)
SOUTHERN Co GAS
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	21.40%	15.00%
ITC and PTC carryforwards
Income Tax Contingency [Line Items]
Tax credit carryforward, amount	$ 1.5		$ 1.8