REGULATORY MATTERS - GAS Schedule of Unrecognized Ratemaking Amounts (Details) - Regulatory Asset Off Balance Sheet - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Atlanta Gas Light
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	$ 47	$ 59
Virginia Natural Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	10	10
Chattanooga Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	4	2
Nicor Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	0	3
Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	$ 61	$ 74