DISPOSITIONS AND DISCONTINUED OPERATIONS (Consolidated Statements of Income) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating revenues:
Operating revenues		$ 587.1	$ 427.6	$ 1,161.1	$ 859.5
Operating expenses:
Commodity costs		496.8	350.5	968.2	685.9
Operating and administrative		28.3	40.0	64.7	74.8
Depreciation and amortization		37.1	40.0	74.5	79.5
Asset impairment		0.0	10.6	0.0	10.6
Operating expenses, Total		622.9	488.5	1,218.2	948.8
Operating loss		(35.8)	(60.9)	(57.1)	(89.3)
Interest expense, net		(9.5)	(8.1)	(17.4)	(16.5)
Other income		10.4	6.5	18.6	13.9
Loss before income tax expense		(34.9)	(62.5)	(55.9)	(91.9)
Income tax expense		(0.5)	(0.5)	(0.9)	(1.4)
Net loss from discontinued operations	[1]	(35.4)	(63.0)	(56.8)	(93.3)
Commodity sales - nonaffiliate [Member]
Operating revenues:
Operating revenues		559.3	379.4	1,085.0	757.2
Commodity sales - affiliate [Member]
Operating revenues:
Operating revenues		3.3	1.4	9.4	6.6
Transportation and other services - nonaffiliate [Member]
Operating revenues:
Operating revenues		24.5	46.8	66.7	95.7
Commodity costs - affiliate [Member]
Operating expenses:
Commodity costs		25.7	8.5	42.1	21.2
Operating and administrative - affiliate [Member]
Operating expenses:
Operating and administrative		$ 35.0	$ 38.9	$ 68.7	$ 76.8

[1] Certain costs that are not allocated to individual segments, including Other, interest expense, allowance for equity used during construction, and income taxes are included in the consolidated total.