REGULATORY MATTERS - APC Rate CNP (Details) - Alabama Power - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule of Regulatory Assets and Liabilities [Line Items]
Under recovered certified power purchase agreements	$ 84	$ 58
Retail revenue requirement for environmental compliance	59	59	$ 68
Over (under) recovered environmental clause	$ (16)	$ 28