Contingencies and Regulatory Matters - Current And Actual Cost Estimate (Details) - Mississippi Power [Member] - USD ($) $ in Millions		9 Months Ended	12 Months Ended
	Apr. 08, 2016	Sep. 30, 2016	Dec. 31, 2012	Dec. 03, 2015
Loss Contingencies [Line Items]
Additional DOE Grants			$ 245
Kemper IGCC [Member]
Loss Contingencies [Line Items]
Plant Subject to Cost Cap		$ 5,300	2,880
Lignite Mine and Equipment		230
CO2 Pipeline Facilities		110
AFUDC		710
Combined Cycle and Related Assets Placed in Service – Incremental		30
General Exceptions		90
Deferred Costs		200
Additional DOE Grants		(140)
Total Kemper IGCC, Actual Costs		$ 6,530
Purchase of Interest		100.00%		15.00%
Government grants received	$ 137
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
Additional DOE Grants		0
Total Kemper IGCC, Actual Costs		2,970
Current Estimate [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Plant Subject to Cost Cap		5,520
Lignite Mine and Equipment		230
CO2 Pipeline Facilities		110
AFUDC		750
Combined Cycle and Related Assets Placed in Service – Incremental		40
General Exceptions		100
Deferred Costs		210
Additional DOE Grants		(140)
Total Kemper IGCC, Actual Costs		$ 6,820
Maximum [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Plant Subject to Cost Cap			$ 2,880