Regulatory Matters - GAS Schedule of Infrastructure Replacement Programs and Capital Projects (Details) - SOUTHERN Co GAS $ in Millions	9 Months Ended
	Sep. 30, 2023 USD ($)
Public Utilities, General Disclosures [Line Items]
Capital expenditures	$ 467
Investing in Illinois
Public Utilities, General Disclosures [Line Items]
Capital expenditures	320
SAVE
Public Utilities, General Disclosures [Line Items]
Capital expenditures	56
System Reinforcement Rider
Public Utilities, General Disclosures [Line Items]
Capital expenditures	84
Pipeline Replacement Program
Public Utilities, General Disclosures [Line Items]
Capital expenditures	$ 7