Goodwill - Changes in Gross Amounts of Goodwill (Details) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Goodwill [Roll Forward]
Beginning balance		$ 417.0		$ 417.0	$ 0.0
Acquisition, February 27, 2015					707.0
Provisional impairment	$ (183.0)	(24.0)	$ (290.0)	(207.0)	(290.0)	$ 0.0
Ending balance	210.0	393.0	417.0	210.0	417.0	0.0
West Texas LPG Pipeline Limited Partnership [Member]
Goodwill [Roll Forward]
Beginning balance		326.9		326.9	0.0
Acquisition, February 27, 2015					364.5
Provisional impairment	(137.8)	(14.4)			(37.6)
Ending balance	174.7		326.9	174.7	326.9	0.0
SouthTX [Member]
Goodwill [Roll Forward]
Beginning balance		90.1		90.1	0.0
Acquisition, February 27, 2015					160.3
Provisional impairment	(45.2)	(9.6)			(70.2)
Ending balance	35.3		90.1	35.3	90.1	0.0
SouthOK [Member]
Goodwill [Roll Forward]
Beginning balance		0.0		0.0	0.0
Acquisition, February 27, 2015					182.2
Provisional impairment	0.0	$ 0.0			(182.2)
Ending balance	$ 0.0		$ 0.0	$ 0.0	$ 0.0	$ 0.0