Income Taxes - Narrative (Details) - USD ($) $ in Billions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	17.50%	13.90%
ITC and PTC carryforwards
Income Tax Contingency [Line Items]
Deferred tax assets	$ 1.2		$ 1.4
GEORGIA POWER CO
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	7.30%	12.30%
SOUTHERN POWER CO
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	(1.60%)	11.30%
SOUTHERN Co GAS
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	36.60%	21.40%