RISK MANAGEMENT ACTIVITIES - CASH FLOW HEDGES (Details) (Cash flow hedges, Holding Company and Other, Interest rate swaps, Interest expense, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flow hedges | Holding Company and Other | Interest rate swaps | Interest expense
Risk management activities
Loss Reclassified from Accumulated OCI into Income (Effective Portion)	$ (1.1)	$ (1.1)	$ (1.1)