Asset Retirement Obligations - Accumulated Provisions for the External Decommissioning Trust Funds (Details) - External decommissioning trust funds - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Georgia Power
Public Utilities, General Disclosures [Line Items]
Accumulated provisions for decommissioning	$ 873	$ 929
Plant Farley | Alabama Power
Public Utilities, General Disclosures [Line Items]
Accumulated provisions for decommissioning	846	902
Plant Hatch | Georgia Power
Public Utilities, General Disclosures [Line Items]
Accumulated provisions for decommissioning	547	583
Plant Vogtle Units 1 and 2 | Georgia Power
Public Utilities, General Disclosures [Line Items]
Accumulated provisions for decommissioning	$ 326	$ 346