Contingencies and Regulatory Matters - IGCC (Details) $ in Millions													1 Months Ended			2 Months Ended	3 Months Ended		5 Months Ended	6 Months Ended			12 Months Ended		38 Months Ended	65 Months Ended
	Jun. 28, 2017 USD ($)	Jun. 21, 2017	Nov. 17, 2016 USD ($)	Jun. 09, 2016 USD ($)	Jun. 03, 2016	Apr. 08, 2016 USD ($)	Dec. 03, 2015 USD ($)	Aug. 13, 2015 USD ($)	Jul. 07, 2015 USD ($)	Jun. 03, 2015 USD ($)	Jan. 01, 2014 USD ($)	Mar. 19, 2013	Jun. 30, 2017 USD ($) mi	Mar. 31, 2016 USD ($)	Jan. 31, 2013 USD ($)	May 31, 2017 USD ($)	Jun. 30, 2017 USD ($) mi	Jun. 30, 2016 USD ($)	May 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($) mi MW	Jun. 30, 2016 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2010	Jun. 30, 2017 USD ($) mi	May 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	May 20, 2015 USD ($)
Loss Contingencies [Line Items]
Unrecognized tax benefits													$ 501				$ 501				$ 501				$ 501		$ 484
MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Plant capacity under coal gasification combined cycle technology | MW																					582
Cost related to grant funding																							$ 245
Maximum cap construction cost																							2,880
Reduced percentage interest transferred under asset purchase agreement												15.00%												15.00%
Public utilities, approved rate increase (decrease), percentage											3.00%
Settlement agreement collection amount to mitigate rate impact, year two											$ 156
Retail rate recovery									$ 342
Carrying costs associated with retail rate recovery									$ 29
AFUDC cost																					$ 22
Interest bearing refundable deposit related to assets sale																												$ 275
Promissory note										$ 301
Unrecognized tax benefits													468				468				468				468		$ 465
Kemper Igcc [Member]
Loss Contingencies [Line Items]
Pre-tax charge to income																	3,000	$ 81			3,100	$ 134
After tax charge to income																	2,100	$ 50			2,200	$ 83
Unrecognized tax benefits													$ 464				$ 464				$ 464				$ 464
Kemper Igcc [Member] | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Purchase of Interest													100.00%				100.00%				100.00%				100.00%
Pipeline infrastructure | mi													61				61				61				61
Estimated cost			$ 68																		$ 5,680		2,880		$ 2,880
Cost related to grant funding																					(140)
Maximum cap construction cost																					$ 7,090
Period of commercial operations established by discovery docket																					5 years
Government grants received						$ 137
Pre-tax charge to income													$ 2,800			$ 196	$ 3,000		$ 305		$ 3,100					$ 3,070
After tax charge to income													2,000			$ 121			$ 188							$ 1,890
Construction and development costs																					1,300
Settlement agreement, term to file		45 days
Period from settlement agreement to hearing		45 days
CIP expenditures incurred but not yet paid																					3,300
Average annual increase (decrease) in operations and maintenance expenses																					105
Average annual increase (decrease) in maintenance capital																					44
Regulatory assets													117				117				117				117
Regulatory liabilities													10				10				10				10
AFUDC cost																									493
Proceeds from bonus depreciation																					370
Proceeds from income tax refunds																					82
Unrecognized tax benefits													464				464				$ 464				464
Kemper Igcc [Member] | MISSISSIPPI POWER CO | Minimum
Loss Contingencies [Line Items]
Amortization period of regulatory assets and liabilities																					2 years
Kemper Igcc [Member] | MISSISSIPPI POWER CO | Maximum
Loss Contingencies [Line Items]
Amortization period of regulatory assets and liabilities																					10 years
Kemper Igcc [Member] | MISSISSIPPI POWER CO | Pending Litigation
Loss Contingencies [Line Items]
Loss contingency, value of damages sought	$ 500			$ 100
Kemper Igcc [Member] | MISSISSIPPI POWER CO | Property, Plant and Equipment
Loss Contingencies [Line Items]
Construction and development costs																					$ 1,200
Kemper Igcc [Member] | MISSISSIPPI POWER CO | Materials And Supplies
Loss Contingencies [Line Items]
Construction and development costs																					14
Kemper Igcc [Member] | MISSISSIPPI POWER CO | Other regulatory assets current
Loss Contingencies [Line Items]
Construction and development costs																					22
Kemper Igcc [Member] | MISSISSIPPI POWER CO | Other regulatory assets, deferred
Loss Contingencies [Line Items]
Construction and development costs																					95
Kemper Igcc [Member] | MISSISSIPPI POWER CO | Transmission and Related Regulatory Assets
Loss Contingencies [Line Items]
Construction and development costs																					800
Kemper Igcc [Member] | MISSISSIPPI POWER CO | Assets, Current
Loss Contingencies [Line Items]
Regulatory assets													$ 22				$ 22				22				22
Electricity Generation Plant, Non-Nuclear | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Estimated cost															$ 2,400								$ 2,400
Kemper IGCC - Combined Cycle | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
CIP expenditures incurred but not yet paid																					$ 500
Percentage of costs contracted to third party																					15.00%
Kemper IGCC - Gasification | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
CIP expenditures incurred but not yet paid																					$ 2,800
AFUDC cost																									$ 459
Mine | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Term of management fee contract																								40 years
Scenario, Forecast | Kemper Igcc [Member] | MISSISSIPPI POWER CO | Minimum
Loss Contingencies [Line Items]
Pre-tax charge to income																				$ 100
Scenario, Forecast | Kemper Igcc [Member] | MISSISSIPPI POWER CO | Maximum
Loss Contingencies [Line Items]
Pre-tax charge to income																				$ 200
In-Service Asset Proposal | Kemper Igcc [Member] | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Approved increase (decrease) in fuel rates amount							$ 126	$ 159
Public utilities, approved equity capital structure, percentage							49.733%
Public utilities, approved return on equity percentage							9.225%
Customer refund														$ 11
Denbury Onshore, Contractor | Kemper Igcc [Member] | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Long term contract for purchase of percentage of carbon dioxide captured from plant					100.00%								70.00%				70.00%				70.00%				70.00%
Treetop Midstream Services, LLC, Contractor | Kemper Igcc [Member] | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Long term contract for purchase of percentage of carbon dioxide captured from plant													30.00%				30.00%				30.00%				30.00%
Denbury Onshore, Contractor | Electricity Generation Plant, Non-Nuclear | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Long-term contract for purchase of carbon dioxide, term					16 years