REGULATORY MATTERS - MPC System Restoration Rider (Details) - USD ($)				1 Months Ended	12 Months Ended
	Dec. 07, 2021	Jun. 08, 2021	Apr. 06, 2021	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Oct. 14, 2021
Public Utilities, General Disclosures [Line Items]
Minimum annual accrual, amount	$ 8,000,000
Major storms
Public Utilities, General Disclosures [Line Items]
Storm damage reserves accrual					$ 286,000,000	$ 326,000,000	$ 170,000,000
Mississippi Power
Public Utilities, General Disclosures [Line Items]
Threshold above which actual damages are charged to the reserve (individually exceed)					50,000
Public utilities, approved rate increase (decrease), amount	9,000,000	$ 16,000,000	$ 28,000,000	$ (16,700,000)
Target property damage reserve	$ 75,000,000
Mississippi Power | Hurricanes Zeta and Ida Accounting Order
Public Utilities, General Disclosures [Line Items]
Regulatory asset								$ 49,000,000
Mississippi Power | Retail electric revenues
Public Utilities, General Disclosures [Line Items]
Property damage reserve					31,000,000	4,000,000
Mississippi Power | Major storms
Public Utilities, General Disclosures [Line Items]
Storm damage reserves accrual					$ (1,800,000)	$ 800,000	$ 1,400,000