CONTINGENCIES, COMMITMENTS, AND GUARANTEES - Guarantees (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Recorded Unconditional Purchase Obligation [Line Items]
Notes payable	$ 2,314	$ 2,609
Alabama Power
Recorded Unconditional Purchase Obligation [Line Items]
Jointly owned affiliate equity	69
Jointly owned affiliate long term debt	100
Notes payable	40	$ 0
SEGCO | Alabama Power
Recorded Unconditional Purchase Obligation [Line Items]
Guarantee of unsecured senior notes	100
Notes payable	$ 0