CONCENTRATIONS OF CREDIT RISK (Details) $ in Millions	Sep. 30, 2015 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	$ 15.7
Net receivable amount	13.4
Utility Companies And Their Affiliates
Concentration Risk [Line Items]
Accounts receivable	21.6
Net receivable amount	20.5
Largest Counterparties
Concentration Risk [Line Items]
Accounts receivable	13.7
Net receivable amount	$ 12.5