DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES (Reconciliation of Changes in Fair Value of L3 Assets and Liabilities on Recurring Basis) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2016 USD ($)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 103.8
Transfer in (out) of Level 3	0.0	[1]
Purchases, issuances, sales and settlements:
Purchases	0.0
Sales	0.0
Settlements	(27.1)	[2]
Ending balance	77.4
Commodity Sales [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gains or losses included in earnings:	(6.7)
Purchases, issuances, sales and settlements:
Amounts reported in Commodity sales	(2.4)
Amount of changes in net assets attributable to the change in derivative gains or losses related to assets and liabilities still held at the reporting date:	(2.7)
Commodity Costs [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gains or losses included in earnings:	7.4
Purchases, issuances, sales and settlements:
Amount of changes in net assets attributable to the change in derivative gains or losses related to assets and liabilities still held at the reporting date:	2.7
Commodity Contracts - Financial [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	8.9
Transfer in (out) of Level 3	0.0	[1]
Purchases, issuances, sales and settlements:
Purchases	0.0
Sales	0.0
Settlements	(3.8)	[2]
Ending balance	5.5
Commodity Contracts - Financial [Member] | Commodity Sales [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gains or losses included in earnings:	0.0
Purchases, issuances, sales and settlements:
Amounts reported in Commodity sales	0.0
Amount of changes in net assets attributable to the change in derivative gains or losses related to assets and liabilities still held at the reporting date:	0.0
Commodity Contracts - Financial [Member] | Commodity Costs [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gains or losses included in earnings:	0.4
Purchases, issuances, sales and settlements:
Amount of changes in net assets attributable to the change in derivative gains or losses related to assets and liabilities still held at the reporting date:	0.4
Commodity Contracts - Physical [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	0.6
Transfer in (out) of Level 3	0.0	[1]
Purchases, issuances, sales and settlements:
Purchases	0.0
Sales	0.0
Settlements	(1.5)	[2]
Ending balance	0.9
Commodity Contracts - Physical [Member] | Commodity Sales [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gains or losses included in earnings:	(6.7)
Purchases, issuances, sales and settlements:
Amounts reported in Commodity sales	(2.4)
Amount of changes in net assets attributable to the change in derivative gains or losses related to assets and liabilities still held at the reporting date:	(2.7)
Commodity Contracts - Physical [Member] | Commodity Costs [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gains or losses included in earnings:	8.5
Purchases, issuances, sales and settlements:
Amount of changes in net assets attributable to the change in derivative gains or losses related to assets and liabilities still held at the reporting date:	4.8
Commodity Option [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	94.3
Transfer in (out) of Level 3	0.0	[1]
Purchases, issuances, sales and settlements:
Purchases	0.0
Sales	0.0
Settlements	(21.8)	[2]
Ending balance	71.0
Commodity Option [Member] | Commodity Sales [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gains or losses included in earnings:	0.0
Purchases, issuances, sales and settlements:
Amounts reported in Commodity sales	0.0
Amount of changes in net assets attributable to the change in derivative gains or losses related to assets and liabilities still held at the reporting date:	0.0
Commodity Option [Member] | Commodity Costs [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gains or losses included in earnings:	(1.5)
Purchases, issuances, sales and settlements:
Amount of changes in net assets attributable to the change in derivative gains or losses related to assets and liabilities still held at the reporting date:	$ (2.5)

[1] Our policy is to recognize transfers as of the last day of the reporting period.

[2] Settlements represent the realized portion of forward contracts.