Regulatory Matters - Kemper County Energy Facility (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	6 Months Ended		48 Months Ended
	Dec. 31, 2018	Jun. 30, 2019	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2023
Loss Contingencies [Line Items]
Liabilities incurred				$ 6
MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Liabilities incurred				0
MISSISSIPPI POWER CO | Kemper IGCC
Loss Contingencies [Line Items]
Pre-tax charge to income		$ 4		6
Asset retirement obligation, liabilities incurred, net of tax		3		5
Asset retirement obligation, expected cost		$ 10		$ 10
Government grants received	$ 387
MISSISSIPPI POWER CO | Kemper IGCC | Scenario, Forecast
Loss Contingencies [Line Items]
Liabilities incurred			$ 7
MISSISSIPPI POWER CO | Kemper IGCC | Minimum | Scenario, Forecast
Loss Contingencies [Line Items]
Liabilities incurred					$ 2
MISSISSIPPI POWER CO | Kemper IGCC | Maximum | Scenario, Forecast
Loss Contingencies [Line Items]
Liabilities incurred					$ 6