STOCK COMPENSATION - Performance Shares, Compensation Costs and Related Tax Benefit (Details) - Performance Shares - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost recognized in income	$ 107	$ 101	$ 112
Tax benefit of compensation cost recognized in income	28	26	29
Southern Company Gas
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost recognized in income	14	12	17
Tax benefit of compensation cost recognized in income	$ 4	$ 4	$ 4