Contingencies and Regulatory Matters - Current And Actual Cost Estimate (Details) - Mississippi Power [Member] - USD ($) $ in Millions		1 Months Ended	12 Months Ended
	Apr. 01, 2015	Jan. 31, 2013	Dec. 31, 2015	Oct. 06, 2014
Loss Contingencies [Line Items]
AFUDC Cost	$ 14		$ 36
Total Kemper IGCC		$ 2,880
Loss Contingency, Estimate of Possible Loss			2,410
Electricity Generation Plant, Non-Nuclear [Member]
Loss Contingencies [Line Items]
Plant Subject to Cost Cap		$ 2,440
Kemper IGCC [Member]
Loss Contingencies [Line Items]
Plant Subject to Cost Cap			4,830
Cost Of Lignite Mine And Equipment			230
Cost Of CO2 Pipeline Facilities			110
Cost Of AFUDC			590
Combined Cycle And Related Assets Placed In Service, Incremental			10
AFUDC Cost	$ 11
Plant General Exceptions			90
Plant Regulatory Asset			170
Total Kemper IGCC			$ 6,030
Purchase of Interest			100.00%	15.00%
Kemper IGCC [Member] | Project Estimate [Member]
Loss Contingencies [Line Items]
Plant Subject to Cost Cap			$ 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
Total Kemper IGCC			2,970
Kemper IGCC [Member] | Current Estimate [Member]
Loss Contingencies [Line Items]
Plant Subject to Cost Cap			5,290
Cost Of Lignite Mine And Equipment			230
Cost Of CO2 Pipeline Facilities			110
Cost Of AFUDC			690
Combined Cycle And Related Assets Placed In Service, Incremental			10
Plant General Exceptions			100
Plant Regulatory Asset			200
Total Kemper IGCC			$ 6,630