Regulatory Matters - APC Reliability Reserve Accounting Matter (Details) - USD ($) $ in Millions	Sep. 30, 2023	Aug. 18, 2023	Dec. 31, 2022
Public Utilities, General Disclosures [Line Items]
Reliability reserve balance	$ 16		$ 216
ALABAMA POWER CO
Public Utilities, General Disclosures [Line Items]
Reliability reserve balance	$ 71		$ 97
Reliability Reserve | ALABAMA POWER CO
Public Utilities, General Disclosures [Line Items]
Reliability reserve balance		$ 166