Contingencies and Regulatory Matters - Current And Actual Cost Estimate (Details) (Mississippi Power [Member], USD $)	0 Months Ended	3 Months Ended		12 Months Ended
	May 07, 2015	Mar. 31, 2015		Dec. 31, 2012
Subsequent Event [Member]
Loss Contingencies [Line Items]
AFUDC Cost	$ 12,000,000
Kemper Igcc [Member]
Loss Contingencies [Line Items]
Estimated Cost		4,370,000,000	[1]	2,880,000,000
Cost Of Lignite Mine And Equipment		230,000,000
CO2 Pipeline Facilities		100,000,000
Cost Of AFUDC		480,000,000	[2],[3]
Combined Cycle And Related Assets Placed In Service, Incremental		0	[4]
General Exceptions		80,000,000
Deferred Costs		140,000,000	[3],[5]
Maximum Cap Construction Cost		5,400,000,000	[1],[3]
Kemper Igcc [Member] | Subsequent Event [Member]
Loss Contingencies [Line Items]
AFUDC Cost	9,000,000
Project Estimate [Member] | Kemper Igcc [Member]
Loss Contingencies [Line Items]
Estimated Cost		2,400,000,000	[1],[6]
Cost Of Lignite Mine And Equipment		210,000,000	[6]
CO2 Pipeline Facilities		140,000,000	[6]
Cost Of AFUDC		170,000,000	[2],[3],[6]
Combined Cycle And Related Assets Placed In Service, Incremental		0	[4],[6]
General Exceptions		50,000,000	[6]
Deferred Costs		0	[3],[5],[6]
Maximum Cap Construction Cost		2,970,000,000	[1],[3],[6]
Current Estimate [Member] | Kemper Igcc [Member]
Loss Contingencies [Line Items]
Estimated Cost		4,940,000,000	[1]
Cost Of Lignite Mine And Equipment		230,000,000
CO2 Pipeline Facilities		110,000,000
Cost Of AFUDC		640,000,000	[2],[3]
Combined Cycle And Related Assets Placed In Service, Incremental		20,000,000	[4]
General Exceptions		100,000,000
Deferred Costs		180,000,000	[3],[5]
Maximum Cap Construction Cost		$ 6,220,000,000	[1],[3]

[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 and exclude post-in-service costs for the lignite mine. See "Rate Recovery of Kemper IGCC Costs – 2013 MPSC Rate Order" for additional information.

[2] 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." The current estimate includes an approximately $9 million increase in AFUDC related to a settlement agreement with the wholesale customers for cost-based rates under FERC's jurisdiction. See "FERC Matters" herein for additional information.

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

[4] Incremental operating and maintenance costs related to the combined cycle and associated common facilities placed in service in August 2014, net of costs related to energy sales. See "Rate Recovery of Kemper IGCC Costs – 2013 MPSC Rate Order" for additional information.

[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.