Contingencies and Regulatory Matters - Current And Actual Cost Estimate (Details) (Details) - MISSISSIPPI POWER CO - USD ($) $ in Millions			6 Months Ended	12 Months Ended	38 Months Ended
	Nov. 17, 2016	Apr. 08, 2016	Jun. 30, 2017	Dec. 31, 2012	Jun. 30, 2017
Loss Contingencies [Line Items]
Cost related to grant funding				$ 245
Maximum cap construction cost				2,880
Kemper IGCC
Loss Contingencies [Line Items]
Estimated cost	$ 68		$ 5,680	$ 2,880	$ 2,880
Cost Of Lignite Mine And Equipment			230
Cost Of CO2 Pipeline Facilities			110
Cost Of AFUDC			850
Combined Cycle And Related Assets Placed In Service, Incremental			50
Plant General Exceptions			80
Government grants received		$ (137)
Plant Regulatory Asset			230
Cost related to grant funding			(140)
Maximum cap construction cost			7,090
Deferred costs and other assets			1		1
Project Estimate [Member] | Kemper IGCC
Loss Contingencies [Line Items]
Estimated cost			2,400
Cost Of Lignite Mine And Equipment			210
Cost Of CO2 Pipeline Facilities			140
Cost Of AFUDC			170
Combined Cycle And Related Assets Placed In Service, Incremental			0
Plant General Exceptions			50
Plant Regulatory Asset			0
Cost related to grant funding			0
Maximum cap construction cost			2,970
Current Estimate [Member] | Kemper IGCC
Loss Contingencies [Line Items]
Estimated cost			5,950
Cost Of Lignite Mine And Equipment			230
Cost Of CO2 Pipeline Facilities			110
Cost Of AFUDC			850
Combined Cycle And Related Assets Placed In Service, Incremental			50
Plant General Exceptions			100
Plant Regulatory Asset			230
Cost related to grant funding			(140)
Maximum cap construction cost			7,380
Deferred costs and other assets			$ 33		$ 33