DERIVATIVES - Narrative (Details) MMBTU in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) MMBTU	Dec. 31, 2021 USD ($)
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	23
Estimated pre-tax gains (losses) that will be reclassified from OCI to interest expense for the next 12-month period	$ (16,000,000)
Collateral already posted, aggregate fair value	41,000,000
Estimated pre-tax gains (losses) expected to be reclassified from AOCI	$ (27,000,000)
Alabama Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	6
Collateral already posted, aggregate fair value	$ 0
Georgia Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	8
Mississippi Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	3
Southern Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	6
Estimated pre-tax gains (losses) that will be reclassified from OCI to interest expense for the next 12-month period	$ 11,000,000
Collateral already posted, aggregate fair value	15,000,000
Estimated pre-tax gains (losses) expected to be reclassified from AOCI	(11,000,000)
Registrants | Derivative Counterparties
Derivative [Line Items]
Collateral already posted, aggregate fair value	0
Southern Company Gas [Member]
Derivative [Line Items]
Collateral already posted, aggregate fair value	41,000,000	$ 3,000,000
Estimated pre-tax gains (losses) expected to be reclassified from AOCI	$ (16,000,000)