REGULATORY MATTERS - APC Accounting Orders and Plant Greene County (Details) - USD ($) $ in Millions	Dec. 31, 2021	Sep. 09, 2021	Dec. 31, 2020
Public Utilities, General Disclosures [Line Items]
Other deferred charges and assets	$ 17,259		$ 16,298
Alabama Power
Public Utilities, General Disclosures [Line Items]
Other deferred charges and assets	$ 4,549		4,262
Percent ownership	14.00%
Alabama Power | Software Accounting Order
Public Utilities, General Disclosures [Line Items]
Other deferred charges and assets	$ 35		17
Mississippi Power
Public Utilities, General Disclosures [Line Items]
Other deferred charges and assets	$ 877		$ 805
Mississippi Power | Plant Greene County Units 1 and 2
Public Utilities, General Disclosures [Line Items]
Percent ownership		40.00%