Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Income Tax Contingency [Line Items]
Effective tax (benefit) rate		13.90%	20.00%
ALABAMA POWER CO
Income Tax Contingency [Line Items]
Effective tax (benefit) rate		8.30%	23.70%
GEORGIA POWER CO
Income Tax Contingency [Line Items]
Effective tax (benefit) rate		18.20%	18.50%
Unrecognized tax positions		$ 86.0
MISSISSIPPI POWER CO
Income Tax Contingency [Line Items]
Effective tax (benefit) rate		16.90%	20.10%
SOUTHERN POWER CO
Income Tax Contingency [Line Items]
Effective tax (benefit) rate		14.80%	18.80%
SOUTHERN POWER CO | ITC and PTC carryforwards
Income Tax Contingency [Line Items]
Deferred tax assets		$ 1,000.0		$ 1,100.0
Southern Company parent
Income Tax Contingency [Line Items]
Unrecognized tax positions		$ 167.0		$ 80.0
Southern Company parent | Scenario, Forecast
Income Tax Contingency [Line Items]
Tax position as a result of expiration of statue of limitations	$ 44.0