Income Taxes (Details) - USD ($) $ in Billions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	30.20%	22.70%
GEORGIA POWER CO
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	22.60%	25.50%
MISSISSIPPI POWER CO
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	16.30%	20.80%
SOUTHERN POWER CO
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	(13.60%)	(220.30%)
SOUTHERN Co GAS
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	15.00%	61.80%
Investment Tax Credit Carryforward
Income Tax Contingency [Line Items]
Federal ITC/PTC carryforward	$ 1.8		$ 2.4