REGULATORY MATTERS - GAS Schedule of Unrecognized Ratemaking Amounts (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	$ 66	$ 216
Regulatory Asset Off Balance Sheet | Atlanta Gas Light
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	23	35
Regulatory Asset Off Balance Sheet | Virginia Natural Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	10	10
Regulatory Asset Off Balance Sheet | Chattanooga Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	7	2
Regulatory Asset Off Balance Sheet | Nicor Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	3	3
Regulatory Asset Off Balance Sheet | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	$ 43	$ 50