REGULATORY ENVIRONMENT - MGU 2021 RATE APPLICATION (Details) - Michigan Public Service Commission (MPSC) - MGU - USD ($) $ in Millions	Sep. 09, 2021	Jul. 01, 2020
Public Utilities, General Disclosures [Line Items]
Depreciation and interest expense approved for deferral		$ 5.0
Approved rate increase	$ 9.3
Approved rate increase (as a percent)	6.35%
Approved return on equity (as a percent)	9.85%
Approved common equity component average (as a percent)	51.50%
Planned capital investment	$ 31.7