Contingencies and Regulatory Matters - Textual - Litigation, Bonus Depreciation, Investment Tax Credits, and Section 174 (Details) - USD ($) $ in Millions			12 Months Ended			36 Months Ended
	Jun. 09, 2016	Apr. 19, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Loss Contingencies [Line Items]
Unrecognized tax benefits					$ 484		$ 433	$ 170	$ 7
Mississippi Power [Member]
Loss Contingencies [Line Items]
Minimum Percentage of Carbon Dioxide That Must Capture and Sequester to Remain Eligible for Tax Credits		65.00%
Unrecognized tax benefits					465		$ 421	$ 165	$ 4
Kemper IGCC [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Positive Impact From Bonus Depreciation					20
Internal Revenue Code Section Forty Eight Tax Credits Phase I					133
Internal Revenue Code Section Forty Eight Tax Credits Phase I I					279
Unrecognized tax benefits					$ 464
Scenario, Forecast [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Bonus Depreciation for Property Acquired			30.00%	40.00%		50.00%
Scenario, Forecast [Member] | Kemper IGCC [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Positive Impact From Bonus Depreciation						$ 370
Pending Litigation [Member] | Kemper IGCC [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Loss Contingency, Damages Sought, Value	$ 100