Regulatory Matters - Mississippi Power (Details) - USD ($) $ in Millions	Jan. 01, 2019	Jul. 09, 2019
MISSISSIPPI POWER CO | Subsequent Event
Loss Contingencies [Line Items]
Proportionate ownership share		50.00%
Total estimated cost		$ 66.0
MISSISSIPPI POWER CO | Subsequent Event | Ash Pond Closure
Loss Contingencies [Line Items]
Total estimated cost		17.0
MISSISSIPPI POWER CO | MRA Revenue
Loss Contingencies [Line Items]
Decrease in base rate under cost based electric tariff	$ 3.7
Mississippi Power And Gulf Power | Subsequent Event
Loss Contingencies [Line Items]
Total estimated cost		$ 125.0