SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Storm Damage and Reliability Reserves (Details) - USD ($) $ in Millions		12 Months Ended			24 Months Ended
	Jan. 01, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2022	Apr. 04, 2023	Apr. 03, 2023
Liability for Catastrophe Claims [Line Items]
Reliability reserve, amount deferred		$ 63.0	$ 191.0		$ 191.0
Alabama Power
Liability for Catastrophe Claims [Line Items]
Additional accruals authorized by state PSCs				$ 65.0
Reliability reserve, amount deferred		52.0	166.0		166.0
Alabama Power | Weather-related damages
Liability for Catastrophe Claims [Line Items]
Charges against storm damage reserves		24.0
Georgia Power
Liability for Catastrophe Claims [Line Items]
Storm damage reserves	$ 31.0				213.0
Georgia Power | Weather-related damages
Liability for Catastrophe Claims [Line Items]
Charges against storm damage reserves		82.0
Mississippi Power
Liability for Catastrophe Claims [Line Items]
Reliability reserve, amount deferred		11.0	25.0		$ 25.0	$ 11.7	$ 8.3
Mississippi Power | Weather-related damages
Liability for Catastrophe Claims [Line Items]
Charges against storm damage reserves		0.0
Major storms
Liability for Catastrophe Claims [Line Items]
Storm damage reserves			239.0	286.0
Major storms | Alabama Power
Liability for Catastrophe Claims [Line Items]
Additional accruals authorized by state PSCs				65.0
Storm damage reserves			19.0	75.0
Major storms | Georgia Power
Liability for Catastrophe Claims [Line Items]
Storm damage reserves			213.0	213.0
Major storms | Mississippi Power
Liability for Catastrophe Claims [Line Items]
Storm damage reserves		$ 11.7	$ 6.9	$ (1.8)