Contingencies and Regulatory Matters - Current And Actual Cost Estimate (Details) - Mississippi Power [Member] - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Apr. 08, 2016	Mar. 31, 2016	Dec. 31, 2012	Oct. 06, 2014
Loss Contingencies [Line Items]
Cost Related to Grant Funding			$ 245
Kemper IGCC [Member]
Loss Contingencies [Line Items]
Plant Subject to Cost Cap		$ 4,990	$ 2,880
Lignite Mine and Equipment		230
CO2 Pipeline Facilities		120
AFUDC		620
Combined Cycle and Related Assets Placed in Service – Incremental		10
General Exceptions		90
Deferred Costs		180
Total Kemper IGCC, Actual Costs		6,240
Cost Related to Grant Funding		$ 0
Purchase of Interest		100.00%		15.00%
Project Estimate [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Plant Subject to Cost Cap		$ 2,400
Lignite Mine and Equipment		210
CO2 Pipeline Facilities		140
AFUDC		170
Combined Cycle and Related Assets Placed in Service – Incremental		0
General Exceptions		50
Deferred Costs		0
Total Kemper IGCC, Actual Costs		2,970
Cost Related to Grant Funding		0
Current Estimate [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Plant Subject to Cost Cap		5,350
Lignite Mine and Equipment		230
CO2 Pipeline Facilities		110
AFUDC		710
Combined Cycle and Related Assets Placed in Service – Incremental		20
General Exceptions		100
Deferred Costs		200
Total Kemper IGCC, Actual Costs		6,580
Cost Related to Grant Funding		$ (140)
Subsequent Event [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Government Grants Received	$ 137