RETIREMENT BENEFITS - 401K Plan Matching Contributions (Details) - Employee Savings Plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	$ 131	$ 124	$ 119
Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	28	26	26
Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	31	29	28
Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	5	5	5
Southern Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	3	3	2
Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	$ 18	$ 17	$ 16