COMMITMENTS AND CONTINGENCIES (Narrative) (Details) $ in Millions		9 Months Ended
	Jun. 15, 2017 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Mar. 31, 2013 USD ($)	Jul. 26, 2010 Miles bbl
Site Contingency [Line Items]
Remaining liabilities		$ 18.1		$ 99.8
Accrual for environmental loss contingencies		57.4		50.8
Estimated total loss of crude oil release		1,215.0
Costs paid associated with crude oil release		74.2	$ 17.3
Government fines and penalties	$ 67.8
Aggregate insurance coverage limit		650.0
Insurance recoveries, since inception		547.0
Remaining aggregate insurance coverage						$ 145.0
Remaining expected insurance recoveries		103.0			$ 85.0
Disputes with Insurers for Which Partial Payment Was Received [Member]
Site Contingency [Line Items]
Insurance recoveries		42.0
Dispute with One Particular Insurer [Member]
Site Contingency [Line Items]
Remaining expected insurance recoveries		85.0
Consent Decree [Member]
Site Contingency [Line Items]
Accrual for environmental loss contingencies				110.0
Civil Penalties [Member]
Site Contingency [Line Items]
Government fines and penalties	61.0
Line 6A Crude Oil Release [Member]
Site Contingency [Line Items]
Government fines and penalties	1.0
Past Removal Costs and Interest [Member]
Site Contingency [Line Items]
Government fines and penalties	$ 5.8
Liability Program [Member]
Site Contingency [Line Items]
Aggregate insurance coverage limit		940.0
Line Six Marshall Leak [Member]
Site Contingency [Line Items]
Remaining liabilities		64.1		$ 138.8
Crude oil released (in barrels) | bbl							20,000
Area impacted by crude oil release | Miles							38
Estimated total loss of crude oil release		1,200.0
Government fines and penalties		$ 68.5