Contingencies and Regulatory Matters - Current And Actual Cost Estimate (Details) - Mississippi Power [Member] - USD ($) $ in Millions				6 Months Ended		12 Months Ended
		Jun. 30, 2015	Apr. 01, 2015	Jun. 30, 2015		Dec. 31, 2012	May. 20, 2015	Dec. 31, 2014	Oct. 06, 2014
Loss Contingencies [Line Items]
Interest Bearing Refundable Deposit Related to Assets Sale		$ 0		$ 0			$ 275	$ 275
Increase (decrease) in AFUDC Cost			$ 11
Kemper Igcc [Member]
Loss Contingencies [Line Items]
Plant Subject to Cost Cap				4,510	[1]	$ 2,880
Lignite Mine and Equipment				230
CO2 Pipeline Facilities				110
Cost Of AFUDC	[2],[3]			520
Combined Cycle And Related Assets Placed In Service, Incremental	[4]			0
General Exceptions				80
Deferred Costs	[2],[5]			150
Maximum Cap Construction Cost	[1],[2]			5,600
Purchase of Interest									15.00%
Increase (decrease) in AFUDC Cost		$ (11)	$ 8
Project Estimate [Member] | Kemper Igcc [Member]
Loss Contingencies [Line Items]
Plant Subject to Cost Cap	[1],[6]			2,400
Lignite Mine and Equipment	[6]			210
CO2 Pipeline Facilities	[6]			140
Cost Of AFUDC	[2],[3],[6]			170
Combined Cycle And Related Assets Placed In Service, Incremental	[4],[6]			0
General Exceptions	[6]			50
Deferred Costs	[2],[5],[6]			0
Maximum Cap Construction Cost	[1],[2],[6]			2,970
Current Estimate [Member] | Kemper Igcc [Member]
Loss Contingencies [Line Items]
Plant Subject to Cost Cap	[1]			4,960
Lignite Mine and Equipment				230
CO2 Pipeline Facilities				110
Cost Of AFUDC	[2],[3]			620
Combined Cycle And Related Assets Placed In Service, Incremental	[4]			20
General Exceptions				100
Deferred Costs	[2],[5]			190
Maximum Cap Construction Cost	[1],[2]			$ 6,230

[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. The Current Estimate and Actual Costs include the 15% undivided interest in the Kemper IGCC that was previously projected to be purchased by SMEPA. On May 20, 2015, SMEPA notified Mississippi Power of its termination of the asset purchase agreement (APA) and requested the return of a total of $275 million of deposits, which was returned with accrued interest on June 3, 2015.

[2] Amounts in the Current Estimate reflect estimated 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." The current estimate includes an approximately $11 million decrease in AFUDC due to a decrease in AFUDC rates resulting from an increase in short-term debt, partially offset by an $8 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.

[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.