Segment Information - Financial Information and Assets (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Reporting
Revenue from contracts with customers		$ 1,779.9		$ 3,541.1
Cost of sales	[1]	(1,325.6)	$ (932.4)	(2,707.1)	$ (1,934.7)
Operating expenses		(113.4)	(102.6)	(222.6)	(206.7)
Gain (loss) on derivative activity		(15.2)	1.6	(14.7)	4.4
Segment profit		325.7	228.6	596.7	444.1
Depreciation and amortization		(145.3)	(142.5)	(283.4)	(270.8)
Impairments		0.0	0.0	0.0	(7.0)
Goodwill		1,542.2	1,542.2	1,542.2	1,542.2	$ 1,542.2
Capital expenditures		218.2	218.5	399.4	466.6
Total identifiable assets		10,783.6		10,783.6		10,537.8
Corporate
Segment Reporting
Revenue from contracts with customers		(318.8)		(547.8)
Cost of sales		318.8	187.6	547.8	354.6
Operating expenses		0.0	0.0	0.0	0.0
Gain (loss) on derivative activity		(15.2)	1.6	(14.7)	4.4
Segment profit		(15.2)	1.6	(14.7)	4.4
Depreciation and amortization		(2.3)	(2.3)	(4.2)	(4.7)
Impairments					0.0
Goodwill		1,119.9	1,119.9	1,119.9	1,119.9
Capital expenditures		1.0	14.5	2.3	23.5
Total identifiable assets		1,254.4		1,254.4		1,268.3
Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		339.8		649.9
Cost of sales		(178.7)	(177.0)	(340.2)	(356.2)
Operating expenses		(45.8)	(42.9)	(90.0)	(86.8)
Gain (loss) on derivative activity		0.0	0.0	0.0	0.0
Segment profit		115.3	105.6	219.7	207.0
Depreciation and amortization		(53.4)	(59.6)	(105.9)	(109.4)
Impairments					0.0
Goodwill		232.0	232.0	232.0	232.0
Capital expenditures		44.7	39.7	110.0	68.0
Total identifiable assets		3,139.3		3,139.3		3,094.8
Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		808.0		1,582.1
Cost of sales		(723.0)	(575.7)	(1,409.7)	(1,140.4)
Operating expenses		(28.0)	(24.6)	(53.6)	(50.0)
Gain (loss) on derivative activity		0.0	0.0	0.0	0.0
Segment profit		57.0	45.4	118.8	92.1
Depreciation and amortization		(30.5)	(29.4)	59.7	(57.5)
Impairments					0.0
Goodwill		0.0	0.0	0.0	0.0
Capital expenditures		16.6	15.6	23.4	48.3
Total identifiable assets		2,391.1		2,391.1		2,408.5
Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		342.8		597.9
Cost of sales		(170.3)	(99.0)	(309.3)	(187.7)
Operating expenses		(20.8)	(14.7)	(41.5)	(28.8)
Gain (loss) on derivative activity		0.0	0.0	0.0	0.0
Segment profit		151.7	68.8	247.1	122.2
Depreciation and amortization		(46.4)	(38.6)	(88.5)	(75.1)
Impairments					0.0
Goodwill		190.3	190.3	190.3	190.3
Capital expenditures		121.0	135.0	219.5	275.7
Total identifiable assets		2,993.8		2,993.8		2,836.7
Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		608.1		1,259.0
Cost of sales		(572.4)	(268.3)	(1,195.7)	(605.0)
Operating expenses		(18.8)	(20.4)	(37.5)	(41.1)
Gain (loss) on derivative activity		0.0	0.0	0.0	0.0
Segment profit		16.9	7.2	25.8	18.4
Depreciation and amortization		(12.7)	(12.6)	(25.1)	(24.1)
Impairments					(7.0)
Goodwill		0.0	0.0	0.0	0.0
Capital expenditures		34.9	13.7	44.2	51.1
Total identifiable assets		1,005.0		1,005.0		$ 929.5
Product sales
Segment Reporting
Revenue from contracts with customers		1,435.1	927.2	2,934.3	1,917.2
Product sales | Corporate
Segment Reporting
Revenue from contracts with customers		0.0	0.0	0.0	0.0
Product sales | Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		56.8	74.6	139.8	159.7
Product sales | Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		750.7	548.7	1,484.1	1,093.2
Product sales | Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		41.5	27.7	91.5	42.2
Product sales | Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		586.1	276.2	1,218.9	622.1
Product sales, Natural gas sales
Segment Reporting
Revenue from contracts with customers		217.4		473.5
Product sales, Natural gas sales | Corporate
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Product sales, Natural gas sales | Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		56.8		139.8
Product sales, Natural gas sales | Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		122.7		247.7
Product sales, Natural gas sales | Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		37.9		86.0
Product sales, Natural gas sales | Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Product sales, NGL sales
Segment Reporting
Revenue from contracts with customers		631.8		1,242.6
Product sales, NGL sales | Corporate
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Product sales, NGL sales | Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Product sales, NGL sales | Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		627.9		1,236.3
Product sales, NGL sales | Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		3.6		5.5
Product sales, NGL sales | Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.3		0.8
Product sales, Crude oil and condensate sales
Segment Reporting
Revenue from contracts with customers		585.9		1,218.2
Product sales, Crude oil and condensate sales | Corporate
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Product sales, Crude oil and condensate sales | Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Product sales, Crude oil and condensate sales | Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.1		0.1
Product sales, Crude oil and condensate sales | Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Product sales, Crude oil and condensate sales | Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		585.8		1,218.1
Product sales—related parties
Segment Reporting
Revenue from contracts with customers		27.2	29.3	30.8	72.0
Product sales—related parties | Corporate
Segment Reporting
Revenue from contracts with customers		(318.8)	(154.0)	(547.8)	(293.2)
Product sales—related parties | Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		149.4	115.5	253.3	222.0
Product sales—related parties | Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		29.0	5.4	34.7	15.6
Product sales—related parties | Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		165.9	62.4	288.8	126.8
Product sales—related parties | Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		1.7	0.0	1.8	0.8
Product sales, Natural gas sales, related party
Segment Reporting
Revenue from contracts with customers		1.9		2.4
Product sales, Natural gas sales, related party | Corporate
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Product sales, Natural gas sales, related party | Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Product sales, Natural gas sales, related party | Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Product sales, Natural gas sales, related party | Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		1.9		2.4
Product sales, Natural gas sales, related party | Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Product sales, NGL sales, related party
Segment Reporting
Revenue from contracts with customers		25.0		27.4
Product sales, NGL sales, related party | Corporate
Segment Reporting
Revenue from contracts with customers		(278.6)		(474.9)
Product sales, NGL sales, related party | Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		134.3		227.3
Product sales, NGL sales, related party | Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		28.9		34.5
Product sales, NGL sales, related party | Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		140.4		240.5
Product sales, NGL sales, related party | Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Product sales, Crude oil and condensate sales, related party
Segment Reporting
Revenue from contracts with customers		0.3		1.0
Product sales, Crude oil and condensate sales, related party | Corporate
Segment Reporting
Revenue from contracts with customers		(40.2)		(72.9)
Product sales, Crude oil and condensate sales, related party | Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		15.1		26.0
Product sales, Crude oil and condensate sales, related party | Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.1		0.2
Product sales, Crude oil and condensate sales, related party | Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		23.6		45.9
Product sales, Crude oil and condensate sales, related party | Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		1.7		1.8
Midstream services
Segment Reporting
Revenue from contracts with customers		142.4	131.9	234.6	259.3
Midstream services | Corporate
Segment Reporting
Revenue from contracts with customers		0.0	0.0	0.0	0.0
Midstream services | Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		25.2	28.2	44.0	56.0
Midstream services | Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		28.3	56.3	63.3	109.4
Midstream services | Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		72.9	33.0	97.6	60.9
Midstream services | Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		16.0	14.4	29.7	33.0
Midstream services, Gathering and transportation
Segment Reporting
Revenue from contracts with customers		56.7		103.9
Midstream services, Gathering and transportation | Corporate
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Gathering and transportation | Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		13.5		26.7
Midstream services, Gathering and transportation | Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		16.7		34.3
Midstream services, Gathering and transportation | Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		25.6		41.2
Midstream services, Gathering and transportation | Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.9		1.7
Midstream services, Processing
Segment Reporting
Revenue from contracts with customers		58.0		71.4
Midstream services, Processing | Corporate
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Processing | Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		9.5		13.3
Midstream services, Processing | Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		1.1		1.7
Midstream services, Processing | Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		47.4		56.4
Midstream services, Processing | Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, NGL services
Segment Reporting
Revenue from contracts with customers		10.3		26.9
Midstream services, NGL services | Corporate
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, NGL services | Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, NGL services | Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		10.3		26.9
Midstream services, NGL services | Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, NGL services | Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Crude services
Segment Reporting
Revenue from contracts with customers		15.0		27.9
Midstream services, Crude services | Corporate
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Crude services | Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Crude services | Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Crude services | Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		(0.1)		0.0
Midstream services, Crude services | Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		15.1		27.9
Midstream services, Other services
Segment Reporting
Revenue from contracts with customers		2.4		4.5
Midstream services, Other services | Corporate
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Other services | Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		2.2		4.0
Midstream services, Other services | Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.2		0.4
Midstream services, Other services | Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Other services | Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.1
Midstream services—related parties
Segment Reporting
Revenue from contracts with customers		175.2	173.6	341.4	332.6
Midstream services—related parties | Corporate
Segment Reporting
Revenue from contracts with customers		0.0	(33.6)	0.0	(61.4)
Midstream services—related parties | Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		108.4	107.2	212.8	212.3
Midstream services—related parties | Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0	35.3	0.0	64.3
Midstream services—related parties | Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		62.5	59.4	120.0	108.8
Midstream services—related parties | Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		4.3	$ 5.3	8.6	$ 8.6
Midstream services, Gathering and transportation, related party
Segment Reporting
Revenue from contracts with customers		100.1		187.4
Midstream services, Gathering and transportation, related party | Corporate
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Gathering and transportation, related party | Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		61.4		114.0
Midstream services, Gathering and transportation, related party | Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Gathering and transportation, related party | Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		38.7		73.4
Midstream services, Gathering and transportation, related party | Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Processing, related party
Segment Reporting
Revenue from contracts with customers		69.9		143.6
Midstream services, Processing, related party | Corporate
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Processing, related party | Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		46.8		98.4
Midstream services, Processing, related party | Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Processing, related party | Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		23.1		45.2
Midstream services, Processing, related party | Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Crude services, related party
Segment Reporting
Revenue from contracts with customers		5.0		10.0
Midstream services, Crude services, related party | Corporate
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Crude services, related party | Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Crude services, related party | Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Crude services, related party | Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.7		1.4
Midstream services, Crude services, related party | Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		4.3		8.6
Midstream services, Other services, related party
Segment Reporting
Revenue from contracts with customers		0.2		0.4
Midstream services, Other services, related party | Corporate
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Other services, related party | Texas | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.2		0.4
Midstream services, Other services, related party | Louisiana | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Other services, related party | Oklahoma | Operating Segments
Segment Reporting
Revenue from contracts with customers		0.0		0.0
Midstream services, Other services, related party | Crude and Condensate | Operating Segments
Segment Reporting
Revenue from contracts with customers		$ 0.0		$ 0.0

[1] Includes related party cost of sales of $46.7 million and $50.9 million for the three months ended June 30, 2018 and 2017, respectively, and $80.8 million and $79.6 million for the six months ended June 30, 2018 and 2017, respectively.