Contingencies and Regulatory Matters - Textual - Integrated Coal Gasification Combined Cycle, Kemper, Lignite Mine, Termination of Proposed Sale (Details)								1 Months Ended		3 Months Ended								12 Months Ended						32 Months Ended	60 Months Ended
	Nov. 17, 2016 USD ($)	Jun. 03, 2016	Jan. 28, 2016 USD ($)	Dec. 03, 2015 USD ($)	Jun. 03, 2015 USD ($)	Jan. 01, 2014 USD ($)	Mar. 19, 2013	Mar. 31, 2016 USD ($)	Jan. 31, 2013 USD ($)	Dec. 31, 2016 USD ($) mi	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) mi MW	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2010	Dec. 31, 2016 USD ($) mi	Dec. 31, 2016 USD ($) mi	Nov. 30, 2016 USD ($)	Jun. 17, 2016 USD ($)	May 03, 2016 USD ($)	Aug. 13, 2015 USD ($)	May 20, 2015 USD ($)
Loss Contingencies [Line Items]
Estimated loss on Kemper IGCC																		$ 428,000,000	$ 365,000,000	$ 868,000,000
Other Regulatory Assets Deferred										$ 6,851,000,000				$ 4,989,000,000				6,851,000,000	4,989,000,000					$ 6,851,000,000	$ 6,851,000,000
Other Assets, Current										230,000,000				71,000,000				230,000,000	71,000,000					230,000,000	230,000,000
Asset Retirement Obligation										4,514,000,000				3,759,000,000				4,514,000,000	3,759,000,000	2,201,000,000				4,514,000,000	4,514,000,000
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity																		202,000,000	226,000,000	245,000,000
Other Regulatory Assets Current										581,000,000				580,000,000				581,000,000	580,000,000					581,000,000	581,000,000
Mississippi Power [Member]
Loss Contingencies [Line Items]
Public Utilities, Property, Plant and Equipment, Construction Work in Progress										$ 3,670,000,000								3,670,000,000						$ 3,670,000,000	$ 3,670,000,000
Estimated loss on Kemper IGCC																		$ 428,000,000	365,000,000	868,000,000
Plant Capacity Under Coal Gasification Combined Cycle Technology | MW																		582
Co Two Pipeline Infrastructure | mi										61								61						61	61
Costs Related to Grant Funding																						$ 245,000,000
Total Kemper IGCC																						$ 2,880,000,000
Other Property And Investments										$ 6,000,000								$ 6,000,000						$ 6,000,000	$ 6,000,000
Lignite Mining Costs										75,000,000								75,000,000						75,000,000	75,000,000
Materials, Supplies, and Other										47,000,000								47,000,000						47,000,000	47,000,000
Cost Deferred in Other Regulatory Assets										29,000,000								29,000,000						29,000,000	29,000,000
Other Regulatory Assets Deferred										518,000,000				525,000,000				518,000,000	525,000,000					518,000,000	518,000,000
Other Assets, Current										8,000,000				8,000,000				8,000,000	8,000,000					8,000,000	8,000,000
Asset Retirement Obligation										179,000,000				177,000,000				179,000,000	177,000,000	$ 48,000,000				179,000,000	179,000,000
Reduced Percentage Interest Transferred under Asset Purchase Agreement																				15.00%			15.00%
PSC Retail Rate Increase (Decrease)																										$ 1,000,000	$ (1,000,000)	$ (2,000,000)
Increase Retail Rates In Year One							15.00%
Increase Retail Rates In Year Two						3.00%
Settlement Agreement Collection Amount To Mitigate Rate Impact Year Two						$ 156,000,000
Retail Rate Recovery														342,000,000					371,000,000
Carrying Costs Associated With Retail Rate Recovery														29,000,000
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity																		124,000,000	110,000,000	$ 136,000,000
Other Regulatory Assets Current										115,000,000				95,000,000				115,000,000	95,000,000					115,000,000	115,000,000
Regulatory Liabilities										$ 7,000,000								$ 7,000,000						$ 7,000,000	$ 7,000,000
Term of Management Fee Contract																		40 years
Percentage of Carbon Dioxide Captured from Project										70.00%								70.00%						70.00%	70.00%
Percentage of Contract to Purchase Carbon Dioxide from Project										30.00%								30.00%						30.00%	30.00%
Interest Bearing Refundable Deposit Related to Assets Sale																														$ 275,000,000
Return Of Interest Bearing Refundable Deposits Related to Assets Sale Plus Accrued Interest					$ 301,000,000
Promissory note			$ 275,000,000		$ 301,000,000													$ 0	301,000,000	0
Electricity Generation Plant, Non-Nuclear [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Estimated Cost									$ 2,400,000,000												$ 2,400,000,000
Kemper IGCC [Member]
Loss Contingencies [Line Items]
Pre-Tax Charge To Income										$ 206,000,000	$ 88,000,000	$ 81,000,000	$ 53,000,000	183,000,000	$ 150,000,000	$ 23,000,000	$ 9,000,000
After Tax Charge To Income										127,000,000	54,000,000	50,000,000	33,000,000	113,000,000	93,000,000	14,000,000	6,000,000	264,000,000	226,000,000	536,000,000
Kemper IGCC [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Estimated loss on Kemper IGCC																									$ 2,840,000,000
Pre-Tax Charge To Income										206,000,000	88,000,000	81,000,000	53,000,000	183,000,000	150,000,000	23,000,000	9,000,000	348,000,000	365,000,000	868,000,000					2,760,000,000
After Tax Charge To Income										$ 127,000,000	$ 54,000,000	$ 50,000,000	$ 33,000,000	$ 113,000,000	$ 93,000,000	$ 14,000,000	$ 6,000,000	$ 215,000,000	$ 226,000,000	536,000,000					$ 1,710,000,000
Purchase of Interest										100.00%								100.00%						100.00%	100.00%
Estimated Cost	$ 68,000,000																	$ 5,440,000,000
Project Improvement Costs										$ 12,000,000								12,000,000						$ 12,000,000	$ 12,000,000
Total Kemper IGCC																		6,730,000,000
Other Regulatory Assets Deferred										172,000,000								172,000,000						172,000,000	172,000,000
Other Assets, Current										3,000,000								3,000,000						3,000,000	3,000,000
Asset Retirement Obligation										14,000,000								14,000,000						14,000,000	14,000,000
Monthly Charge Of Allowance For Equity Funds Used During Construction																		16,000,000
Monthly Cost, Regulatory Assets and Other																		3,000,000
Costs Subject to Cost Cap																		1,990,000,000
Cost Cap Exceptions																		$ 1,460,000,000
Period Of Commercial Operations Established By Discovery Docket																		5 years
Average Annual Increase Decrease in Operations and Maintenance Expenses																		$ 105,000,000
Average Annual Increase Decrease in Maintenance Capital																		44,000,000
Recoverable Cost Above Maximum Cap Construction Cost																		3,310,000,000
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity																								398,000,000
Regulatory asset										97,000,000								97,000,000						97,000,000	97,000,000
Other Regulatory Assets Current										104,000,000								104,000,000						104,000,000	104,000,000
Kemper IGCC [Member] | Parent And Mississippi Power [Member]
Loss Contingencies [Line Items]
Pre-Tax Charge To Income																				868,000,000
After Tax Charge To Income																				$ 536,000,000
Mine [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Term of Management Fee Contract																							40 years
Cost Estimate Extension [Member] | Kemper IGCC [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Estimated Cost																		186,000,000
Operational Readiness And Other Post In-Service Costs [Member] | Kemper IGCC [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Estimated Cost																		162,000,000
Minimum [Member] | Kemper IGCC [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Estimated In-service Capital Cost																		$ 25,000,000
Amortization Period of Regulatory Assets and Liabilities																		2 years
Maximum [Member] | Kemper IGCC [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Estimated In-service Capital Cost																		$ 35,000,000
Amortization Period of Regulatory Assets and Liabilities																		10 years
Wholesale [Member] | Kemper IGCC [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Recoverable Cost Above Maximum Cap Construction Cost, Percent																		29.00%
Retail [Member] | Kemper IGCC [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Recoverable Cost Above Maximum Cap Construction Cost, Percent																		71.00%
2017 Accounting Order Request [Member] | Kemper IGCC [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Monthly Charge Of Allowance For Equity Funds Used During Construction																		$ 11,000,000
Monthly Cost, Regulatory Assets and Other																		25,000,000
2017 Rate Case [Member] | Kemper IGCC [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Pre-Tax Charge To Income																		80,000,000
Alternate Financing																					$ 1,000,000,000
In-Service Asset Proposal [Member] | Kemper IGCC [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Customer Refund								$ 11,000,000
PSC Retail Rate Increase (Decrease)				$ 126,000,000																									$ 159,000,000
Public Utilities, Approved Equity Capital Structure, Percentage				49.733%
Public Utilities, Approved Return on Equity, Percentage				9.225%
Assets, Current [Member] | Kemper IGCC [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Regulatory asset										$ 29,000,000								$ 29,000,000						$ 29,000,000	$ 29,000,000
Denbury Onshore, Contractor [Member] | Kemper IGCC [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Long Term Contract For Purchase Of Percentage of Carbon Dioxide Captured from Plant		100.00%
Denbury Onshore, Contractor [Member] | Electricity Generation Plant, Non-Nuclear [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Long-term Contract For Purchase of Carbon Dioxide, Term		16 years