RETIREMENT BENEFITS - Accumulated Benefit Obligation (Details) - Pension plans - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	$ 11,991	$ 11,422
Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	2,746	2,601
Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	3,674	3,534
Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	546	520
Southern Power
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	145	135
Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	$ 808	$ 801