Regulatory Matters - GAS Schedule of Infrastructure Replacement Programs and Capital Projects (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2023	Dec. 31, 2019
SOUTHERN Co GAS
Public Utilities, General Disclosures [Line Items]
Capital expenditures	$ 294
Investing in Illinois | SOUTHERN Co GAS
Public Utilities, General Disclosures [Line Items]
Capital expenditures	196
Investing in Illinois | Nicor Gas
Public Utilities, General Disclosures [Line Items]
Capital expenditures		$ 415
SAVE | SOUTHERN Co GAS
Public Utilities, General Disclosures [Line Items]
Capital expenditures	37
System Reinforcement Rider | SOUTHERN Co GAS
Public Utilities, General Disclosures [Line Items]
Capital expenditures	57
Pipeline Replacement Program | SOUTHERN Co GAS
Public Utilities, General Disclosures [Line Items]
Capital expenditures	$ 4