REGULATORY MATTERS - MPC Performance Evaluation Plan (Details) - Mississippi Power $ in Millions	1 Months Ended			12 Months Ended
	Jul. 31, 2024 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2022 USD ($)	Dec. 31, 2024 scale filing	Dec. 31, 2021 USD ($)
Public Utilities, General Disclosures [Line Items]
Scale of performance evaluation \| scale				10
Performance evaluation plan, number of filings per calendar year \| filing				2
Public utilities, approved rate increase (decrease), amount \| $	$ (5)	$ (7)	$ 18		$ 9
Approved rate decrease, percent			(1.90%)
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