REGULATORY ENVIRONMENT - MGU 2021 RATE APPLICATION (Details) - Michigan Public Service Commission (MPSC) - MGU - USD ($) $ in Millions		1 Months Ended
	Jul. 29, 2021	Mar. 31, 2021	Jul. 01, 2020
Public Utilities, General Disclosures [Line Items]
Depreciation and interest expense approved for deferral			$ 5.0
Requested rate increase		$ 15.1
Requested rate increase (as a percent)		10.70%
Requested return on equity (as a percent)		10.20%
Requested common equity component average (as a percent)		52.50%
Subsequent event
Public Utilities, General Disclosures [Line Items]
Requested rate increase	$ 9.3
Requested rate increase (as a percent)	6.35%
Requested return on equity (as a percent)	9.85%
Requested common equity component average (as a percent)	51.50%
Planned capital investment	$ 31.7