REGULATORY MATTERS - MPC 2019 Base Rate Case and Performance Evaluation Plan (Details) - Mississippi Power $ in Millions	1 Months Ended				12 Months Ended
	Jun. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)	Jun. 30, 2021 USD ($)	May 31, 2021 USD ($)	Dec. 31, 2022 filing	Dec. 31, 2020 USD ($)
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 decrease, percent	(1.90%)		(1.80%)			1.85%
Base rate case filing, measurement input, average equity ratio						53.00%
Base rate case filing, measurement input, maximum equity ratio						55.00%
Base rate case filing, measurement input, return on investment						7.57%
Regulatory asset amortization period						4 years
Regulatory liability amortization period						3 years
Annual base rate adjustment, increase in depreciation						$ 10.0
Annual base rate adjustment, compensation costs excluded						$ 3.9
Performance evaluation plan, number of filings per calendar year | filing					2
Weighted Average | Measurement Input, Average Customer Price
Public Utilities, General Disclosures [Line Items]
Performance evaluation plan, measurement input					0.40
Weighted Average | Measurement Input, Service Reliability
Public Utilities, General Disclosures [Line Items]
Performance evaluation plan, measurement input					0.40
Weighted Average | Measurement Input, Customer Satisfaction
Public Utilities, General Disclosures [Line Items]
Performance evaluation plan, measurement input					0.20