COMMITMENTS AND CONTINGENCIES (Details) $ in Millions	3 Months Ended		12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017 USD ($)	Dec. 31, 2016	Sep. 30, 2018
Commitments and Contingencies [Line Items]
Number Of Former Manufactured Gas Sites Where We Own Or Retain Legal Responsibility For Environmental Conditions				12
AAO associated with MGP costs requested amount, cap		$ 15.0
Regulatory asset expected to be recorded for MGP costs accrued at January 1, 2017		$ 5.9
Number of sites where we have completed or addressed removal of the source of soil contamination according to plans approved by KDHE.				11
Number of sites with ongoing groundwater monitoring				8
Number of sites where regulatory closure has been achieved				3
Environmental Reserve Estimate Range, Low	5.6		4
Environmental Reserve Estimate Range, High	7		7
Environmental Reserve Estimate, Actual	1.6
Percentage yield of high consequence pipeline areas				30.00%