COMMITMENTS AND CONTINGENCIES (Environmental Liabilities) (Details) $ in Millions	1 Months Ended		2 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015 USD ($) a claims	May. 31, 2015 USD ($) a	Jun. 30, 2015 USD ($) claims	Jun. 30, 2015 USD ($) claims	Jun. 30, 2011 USD ($)	Jun. 30, 2015 USD ($) claims	Jun. 30, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2014 USD ($)	Feb. 25, 2014 bbl	Mar. 31, 2013 USD ($)	Jul. 26, 2010 mi bbl
Remaining liabilities	$ 113.5		$ 113.5	$ 113.5		$ 113.5			$ 141.7
Accrual for environmental loss contingencies	61.9		61.9	61.9		61.9			60.1
Aggregate insurance coverage limit					$ 650.0	860.0
Insurance recoveries				0.8
Insurance recoveries, since inception	547.0		547.0	547.0		547.0
Remaining expected insurance recoveries	103.0		103.0	103.0		103.0
Remaining aggregate insurance coverage											$ 145.0
Disputes with Insurers for Which Partial Payment Was Received [Member]
Insurance recoveries								$ 42.0
Dispute with One Particular Insurer [Member]
Remaining expected insurance recoveries	85.0		85.0	85.0		85.0
Disputes with Remaining Insurers [Member]
Remaining expected insurance recoveries	18.0		18.0	18.0		18.0
Line Six Marshall Leak [Member]
Crude oil released (in barrels) | bbl												20,000
Area impacted by crude oil release (in miles) | mi												38
Remaining liabilities	170.9		170.9	170.9		170.9			$ 195.2
Estimated total loss of crude oil release	$ 1,208.0		$ 1,208.0	$ 1,208.0		1,208.0
Costs paid associated with crude oil release						20.1	$ 65.0
Government fines and penalties						$ 47.5
Loss contingency, pending claims (in claims) | claims	5		5	5		5
Line Six Marshall Leak [Member] | Fines Related to Clean Water Act [Member]
Government fines and penalties						$ 40.0
Line Six Marshall Leak [Member] | May 2015 Settlement [Member]
Costs paid associated with crude oil release		$ 5.0
Area of remediation site (in acres) | a		300
Line Six Marshall Leak [Member] | Reimburse State of Michigan for Costs [Member]
Costs paid associated with crude oil release			$ 12.0
Line Six Marshall Leak [Member] | June 2015 Agreement [Member]
Accrual for environmental loss contingencies	$ 3.9		$ 3.9	$ 3.9		$ 3.9
Area of remediation site (in acres) | a	175
Griffith Terminal Leak [Member]
Crude oil released (in barrels) | bbl										975