REGULATORY MATTERS - MPC Wholesale Regulatory Matters (Details) - Mississippi Power - USD ($) $ in Millions		12 Months Ended
Jan. 01, 2019	Dec. 31, 2019
Cooperative Energy
Public Utilities, General Disclosures [Line Items]
Period of notice to cancel counterparty		10 years
Counterparty's option to decrease services, percentage		2.50%
Counterparty's option to reduce services, maximum percentage		11.00%
Counterparty's option to reduce services, maximum		$ 9.0
MRA Revenue
Public Utilities, General Disclosures [Line Items]
Decrease in base rate under cost based electric tariff due to settlement	$ 3.7

Decrease In Base Rate Under Cost Based Electric Tariff Due To Settlement

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MRA Tariff, Terms, Counterparty's Option To Reduce Use Of Services, Cumulative Annual, Amount

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MRA Tariff, Terms, Counterparty's Option To Reduce Use Of Services, Maximum Total Reduction, Percentage

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MRA Tariff, Terms, Counterparty's Option To Reduce Use Of Services, Percentage

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Period Of Notice To Cancel Counterparty

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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