Contingencies and Regulatory Matters - Current And Actual Cost Estimate (Details) (Kemper Igcc [Member], Mississippi Power [Member], USD $) In Billions, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2014		Dec. 31, 2012
Loss Contingencies [Line Items]
Estimated Cost	$ 4.06	[1]	$ 2.88
Lignite Mine and Equipment	0.23
CO2 Pipeline Facilities	0.10
AFUDC	0.41	[2],[3]
Combined Cycle and Related Assets Placed in Service - Incremental	0	[4]
General Exceptions	0.07
Regulatory Asset	0.10	[2],[5]
Total Kemper IGCC	4.97	[1],[2]
Project Estimate [Member]
Loss Contingencies [Line Items]
Estimated Cost	2.40	[1],[6]
Lignite Mine and Equipment	0.21	[6]
CO2 Pipeline Facilities	0.14	[6]
AFUDC	0.17	[2],[3],[6]
Combined Cycle and Related Assets Placed in Service - Incremental	0	[4],[6]
General Exceptions	0.05	[6]
Regulatory Asset	0	[2],[5],[6]
Total Kemper IGCC	2.97	[1],[2],[6]
Current Estimate [Member]
Loss Contingencies [Line Items]
Estimated Cost	4.86	[1]
Lignite Mine and Equipment	0.23
CO2 Pipeline Facilities	0.11
AFUDC	0.62	[2],[3]
Combined Cycle and Related Assets Placed in Service - Incremental	0	[4]
General Exceptions	0.10
Regulatory Asset	0.18	[2],[5]
Total Kemper IGCC	$ 6.10	[1],[2]

[1] The 2012 MPSC CPCN Order approved a construction cost cap of up to $2.88 billion, net of the DOE Grants and excluding the Cost Cap Exceptions. The Current Estimate and Actual Costs include non-incremental operating and maintenance costs related to the combined cycle and associated common facilities placed in service in August 2014 that are subject to the $2.88 billion cost cap.

[2] Amounts in the Current Estimate reflect costs through March 31, 2016.

[3] Mississippi Power's original estimate included recovery of financing costs during construction rather than the accrual of AFUDC. This approach was not approved by the Mississippi PSC in 2012 as described in "Rate Recovery of Kemper IGCC Costs."

[4] Incremental operating and maintenance costs related to the combined cycle and associated common facilities placed in service on August 9, 2014, net of costs related to energy sales.

[5] The 2012 MPSC CPCN Order approved deferral of non-capital Kemper IGCC-related costs during construction as described in "Rate Recovery of Kemper IGCC Costs – Regulatory Assets and Liabilities."

[6] The 2010 Project Estimate is the certificated cost estimate adjusted to include the certificated estimate for the CO2 pipeline facilities which was approved in 2011 by the Mississippi PSC.