ACQUISITIONS - FORWARD WIND ENERGY CENTER (Details) - Forward Wind Energy Center Acquisition $ in Millions	1 Months Ended	6 Months Ended
	Apr. 30, 2018 wind_turbines utility MW	Jun. 30, 2019 USD ($)
Business Acquisition [Line Items]
Number of utilities along with WPS that entered in an agreement to purchase Forward Wind Energy Center | utility	2
Number of wind turbines at Forward Wind Energy Center | wind_turbines	86
Capacity of Foward Wind Energy Center | MW	138
Purchase price | $		$ 172.9
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 | $		$ 77.1
WPS's share of Forward Wind Energy Center's purchase price	44.60%
Percentage of Forward Wind Energy Center's output purchased by WPS	44.60%