Regulatory Matters - GAS Schedule of Infrastructure Replacement Programs and Capital Projects (Details) - SOUTHERN Co GAS $ in Millions	3 Months Ended
	Mar. 31, 2023 USD ($)
Public Utilities, General Disclosures [Line Items]
Capital expenditures	$ 115
Investing in Illinois
Public Utilities, General Disclosures [Line Items]
Capital expenditures	62
SAVE
Public Utilities, General Disclosures [Line Items]
Capital expenditures	20
System Reinforcement Rider
Public Utilities, General Disclosures [Line Items]
Capital expenditures	32
Pipeline Replacement Program
Public Utilities, General Disclosures [Line Items]
Capital expenditures	$ 1