REGULATORY MATTERS - MPC Fuel Cost Recovery and Ad Valorem Tax Adjustment (Details) - Mississippi Power - USD ($) $ in Millions			1 Months Ended												12 Months Ended
	Feb. 14, 2023	Jan. 10, 2023	Jun. 30, 2023	Jan. 31, 2023	Jul. 31, 2022	Jun. 30, 2022	Feb. 28, 2022	Jan. 31, 2022	Dec. 31, 2021	Jun. 30, 2021	May 31, 2021	Feb. 28, 2021	Jan. 31, 2021	Feb. 29, 2020	Dec. 31, 2020	Dec. 31, 2022	Apr. 30, 2020
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount						$ 18.0			$ 9.0	$ 16.0	$ 28.0				$ (16.7)
Approved rate increase, percent						1.90%				1.80%					(1.85%)
PSC retail increase																	$ 10.0
Public utilities, valorem taxes previously recovered, amount											$ 19.0
Ad Valorem Tax Adjustment
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount					$ 5.0
Subsequent Event
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount	$ 12.0
Retail electric revenues
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount							$ 43.0					$ 2.0		$ (24.0)
Over recovered fuel cost									4.0							$ 1.0
Retail electric revenues | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount		$ 25.0
Retail electric revenues | Scenario, Forecast | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount			$ 25.0
MRA Revenue
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount								$ 11.0					$ (5.0)
Under recovered fuel cost									$ 1.0							$ 6.0
MRA Revenue | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount				$ 22.0