INCOME TAXES (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended	12 Months Ended
	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Dec. 31, 2018	Jun. 30, 2019
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%	35.00%
Reduction in income tax expense for the amortization of the regulatory liability associated with excess ADIT that was returned to customers			$ 10.3
Reduction to revenues due to the change in tax rates collected in our rates				$ 36.6
Oklahoma Natural Gas tax reform regulatory liability				$ 15.8
Change in KGS tax reform regulatory liability [Line Items]	$ 2.4
Kansas Gas Service tax reform regulatory liability					$ 16.6
Texas Gas Service one-time refunds related to tax reform		$ 6.6