REGULATORY MATTERS - Kemper Regulatory Matters (Details) $ in Millions				1 Months Ended		3 Months Ended			6 Months Ended	12 Months Ended					48 Months Ended	65 Months Ended	108 Months Ended
	Dec. 31, 2019	Feb. 07, 2018	Feb. 06, 2018 USD ($)	Apr. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) MW	Dec. 31, 2018 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2023 USD ($)	May 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2010 USD ($)
Schedule of Regulatory Assets and Liabilities [Line Items]
Period costs												$ 37.0	$ 29.0
Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Plant capacity under coal gasification combined cycle technology | MW												582
Maximum cap construction costs														$ 2,880.0
Pre-tax charge to income						$ (9.0)
After tax charge to income						$ (95.0)
Period costs												$ 1.0	0.0
Public utilities, approved return on equity		9.33%
Mississippi Power | Kemper IGCC
Schedule of Regulatory Assets and Liabilities [Line Items]
Firm transportation agreement, term	15 years
Maximum cap construction costs					$ 5,950.0
Estimated cost					7,380.0
Cost related to grant funding					137.0
Pre-tax charge to income					2,800.0		$ 44.0		$ 242.0			$ 24.0	37.0			$ 3,070.0
After tax charge to income					$ 2,000.0		$ 33.0		206.0							$ 1,890.0
After tax charge to income, cost during suspension period									$ 164.0
Period costs, net of tax													$ 68.0
Public utilities, approved rate increase (decrease), amount			$ 99.3
Public utilities, approved return on equity			8.60%
Amortization of regulatory assets												8 years
Amortization of regulatory liabilities												6 years
Disallowance pre-tax charge to income								$ 78.0
Pre-tax charge to income before accumulated depreciation								85.0
Pre-tax charge to income, accumulated depreciation								7.0
Disallowance after tax charge to income								$ 48.0
Reduction in customer rates annually				$ 26.8
Government grants expected																		$ 137.0	$ 270.0
Government grants received																	$ 387.0
Mississippi Power | Kemper IGCC | Scenario, Forecast
Schedule of Regulatory Assets and Liabilities [Line Items]
Period costs										$ 5.0	$ 17.0
Minimum | Mississippi Power | Kemper IGCC | Scenario, Forecast
Schedule of Regulatory Assets and Liabilities [Line Items]
Period costs															$ 15.0
Maximum | Mississippi Power | Kemper IGCC | Scenario, Forecast
Schedule of Regulatory Assets and Liabilities [Line Items]
Period costs															$ 16.0
Department Of Energy, Initial Grants | Mississippi Power | Kemper IGCC
Schedule of Regulatory Assets and Liabilities [Line Items]
Government grants received																	382.0
Department Of Energy, Additional Grants For Future Rate Impacts | Mississippi Power | Kemper IGCC
Schedule of Regulatory Assets and Liabilities [Line Items]
Government grants received																	$ 5.0