REGULATORY MATTERS - APC Rate CNP (Details) - Alabama Power - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule of Regulatory Assets and Liabilities [Line Items]
Under recovered certified power purchase agreements	$ 120	$ 103	$ 120
Retail revenue requirement for environmental compliance		$ 23	$ 255	$ 59
Retail revenue requirement for environmental compliance, as a percentage		(0.30%)	3.70%
Over (under) recovered environmental clause	(47)	$ (33)	$ (47)
Public utilities, approved rate increase (decrease), amount	$ 318
Approved rate increase, percent	4.60%
Other regulatory assets, current
Schedule of Regulatory Assets and Liabilities [Line Items]
Under recovered certified power purchase agreements	$ 18	18	18
Over (under) recovered environmental clause		(8)
Other regulatory assets, deferred
Schedule of Regulatory Assets and Liabilities [Line Items]
Under recovered certified power purchase agreements	$ 102	85	$ 102
Over (under) recovered environmental clause		$ (25)