Contingencies - Environmental Remediation (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
GEORGIA POWER CO
Loss Contingencies [Line Items]
Environmental remediation liability, current and former sites	$ 19	$ 15
SOUTHERN Co GAS
Loss Contingencies [Line Items]
Environmental remediation liability, current and former sites	$ 255	$ 245

Carrying amount of the liability for remediation of environmental damage pertaining to assets or businesses previously disposed.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 5.Y.Q4)
-URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751

Name:	us-gaap_EnvironmentalExitCostsAssetsPreviouslyDisposedLiabilityForRemediation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant