ACQUISITIONS - FORWARD ACQUISITION (Details) - Forward Wind Energy Center $ in Millions	1 Months Ended
	Apr. 30, 2018 USD ($) utility	Apr. 02, 2018 wind_turbines MW	Mar. 31, 2018
WPS
Business Acquisition [Line Items]
Percentage of Forward Wind Energy Center's output purchased by WPS			44.60%
Subsequent event
Business Acquisition [Line Items]
Number of wind turbines at Forward Wind Energy Center | wind_turbines		86
Capacity of Foward Wind Energy Center | MW		129
Purchase price	$ 173.9
Subsequent event | WPS
Business Acquisition [Line Items]
Number of utilities along with WPS that entered in an agreement to purchase Forward Wind Energy Center | utility	2
Purchase price	$ 77.6
WPS's share of Forward Wind Energy Center's purchase price	44.60%