FINANCING - Outstanding Classes of Capital Stock Narrative (Details) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) shares
Debt Instrument [Line Items]
Stock issued employee and director stock plans (in shares)	2.1
Proceeds from issuance of shares under share-based compensation plans | $	$ 36
Number of shares reserved for issuance to stock-based compensation plan (in shares)	131.0
Southern Company Common Stock
Debt Instrument [Line Items]
Remaining shares available for awards (in shares)	26.9