Contingencies - Environmental Remediation (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
GEORGIA POWER CO
Loss Contingencies [Line Items]
Environmental remediation liability, current and former sites	$ 16	$ 23
SOUTHERN Co GAS
Loss Contingencies [Line Items]
Environmental remediation liability, current and former sites	278	$ 294
SOUTHERN Co GAS | Location One
Loss Contingencies [Line Items]
Environmental remediation liability, current and former sites	$ 2