DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES (Effect of Derivative Instruments on Consolidated Statements of Income) (Details) - Derivatives Not Designated As Hedging Instruments [Member] - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Earnings	[1],[2]	$ 0.2	$ (2.7)
Transportation And Other Services Revenue [Member] | Commodity Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Earnings	[1],[2],[3]	0.8	2.7
Gain (Loss) on Settlement of Derivative Instruments		2.5	6.6
Commodity Sales [Member] | Commodity Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Earnings	[1],[2]	(2.4)	(17.3)
Commodity Sales - Affiliate [Member] | Commodity Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Earnings	[1],[2]	0.0	(0.2)
Commodity Costs [Member] | Commodity Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Earnings	[1],[2],[4]	1.8	7.1
Gain (Loss) on Settlement of Derivative Instruments		26.5	25.7
Other Income/(Expense) [Member] | Other Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Earnings	[1],[2]	$ 0.0	$ 5.0

[1] Does not include settlements associated with derivative instruments that settle through physical delivery.

[2] Includes only net gains or losses associated with those derivatives that do not receive hedge accounting treatment and does not include the ineffectives portion of derivatives that are designated as hedging instruments.

[3] Includes settlement gains of $2.5 million and $6.6 million for the three months ended March 31, 2016 and 2015, respectively.

[4] Includes settlement gains of $26.5 million and $25.7 million for the three months ended March 31, 2016 and 2015, respectively.