CONCENTRATIONS OF CREDIT RISK (Details) $ in Millions	Sep. 30, 2016 USD ($) counterparty
Concentration Risk [Line Items]
Number of large counterparties for which credit risk is disclosed | counterparty	5
Energy Producers And Their Affiliates
Concentration Risk [Line Items]
Accounts receivable	$ 15.8
Net receivable amount	12.4
Utility Companies And Their Affiliates
Concentration Risk [Line Items]
Accounts receivable	52.8
Net receivable amount	50.5
Largest Counterparties
Concentration Risk [Line Items]
Accounts receivable	31.2
Net receivable amount	$ 27.2