RELATED PARTIES (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Related parties
Current portion of notes payable to Integrys	$ 0.0	$ 2.9
ATC
Related parties
Accounts receivable for services provided to ATC	0.6	0.5
Accounts payable to ATC for network transmission services	9.2	8.5
Integrys
Related parties
Liability related to income tax allocation	4.9	5.4
Integrys | WPS Leasing
Related parties
Current portion of notes payable to Integrys	$ 0.0	$ 2.9