Regulatory Matters - GAS Schedule of Infrastructure Replacement Programs and Capital Projects (Details) - SOUTHERN Co GAS $ in Millions	6 Months Ended
	Jun. 30, 2021 USD ($)
Public Utilities, General Disclosures [Line Items]
Capital expenditures	$ 201
Investing in Illinois
Public Utilities, General Disclosures [Line Items]
Capital expenditures	179
Steps to Advance Virginia's Energy
Public Utilities, General Disclosures [Line Items]
Capital expenditures	$ 22