REGULATORY MATTERS - APC Rate NDR and Reliability Reserve Accounting Order (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Sep. 30, 2022	Jul. 12, 2022
Public Utilities, General Disclosures [Line Items]
Reliability reserve, amount deferred	$ 63,000,000	$ 63,000,000	$ 191,000,000
Net regulatory assets	6,523,000,000	6,523,000,000	5,833,000,000
Plant in service, net of depreciation	90,703,000,000	90,703,000,000	82,232,000,000
Other utility plant, net	499,000,000	499,000,000	599,000,000
Other regulatory assets	1,120,000,000	1,120,000,000	860,000,000
Reliability reserves
Public Utilities, General Disclosures [Line Items]
Net regulatory assets	(179,000,000)	(179,000,000)	(191,000,000)
Revision of Prior Period, Reclassification, Adjustment
Public Utilities, General Disclosures [Line Items]
Plant in service, net of depreciation			(42,000,000)		$ (600,000,000)
Other utility plant, net					$ 600,000,000
Other regulatory assets			42,000,000
Alabama Power
Public Utilities, General Disclosures [Line Items]
Minimum natural disaster reserve balance, triggering establishment charge	50,000,000	50,000,000
Natural disaster reserve authorized limit	75,000,000	75,000,000				$ 35,000,000
Reliability reserve, amount deferred	52,000,000	52,000,000	166,000,000
Net regulatory assets	2,720,000,000	2,720,000,000	2,340,000,000
Maximum rate NDR charge per month, monthly nonresidential customer account	5	5				10.00
Maximum rate NDR charge per month, monthly residential customer account	2.50	2.50				$ 5.00
Additional accruals authorized by state PSCs				$ 65,000,000
Annual recovery amount		12,000,000	14,000,000	$ 6,000,000
Regulatory asset, amortization period	76,000,000	76,000,000	97,000,000
NDR, expected recovery amount		12,000,000
Plant in service, net of depreciation	24,298,000,000	24,298,000,000	23,002,000,000
Other utility plant, net	499,000,000	499,000,000	599,000,000
Other regulatory assets	385,000,000	385,000,000	372,000,000
Alabama Power | Reliability reserves
Public Utilities, General Disclosures [Line Items]
Net regulatory assets	(143,000,000)	$ (143,000,000)	$ (166,000,000)
Accrual	$ 75,000,000
Alabama Power | Minimum
Public Utilities, General Disclosures [Line Items]
Maximum period for recovery deferred stock related operations and maintenance costs and any future reserve deficits		24 months
Alabama Power | Maximum
Public Utilities, General Disclosures [Line Items]
Maximum period for recovery deferred stock related operations and maintenance costs and any future reserve deficits		48 months