Income Taxes - Federal ITC/PTC Carryforwards (Details) - ITC and PTC carryforward $ in Millions	Dec. 31, 2018 USD ($)
Operating Loss Carryforwards [Line Items]
Federal ITC/PTC carryforwards	$ 2,410
Alabama Power
Operating Loss Carryforwards [Line Items]
Federal ITC/PTC carryforwards	11
Georgia Power
Operating Loss Carryforwards [Line Items]
Federal ITC/PTC carryforwards	108
Southern Power
Operating Loss Carryforwards [Line Items]
Federal ITC/PTC carryforwards	$ 2,128