(Deficit) Equity - Private Placement (Details) - USD ($) $ / shares in Units, $ in Millions					3 Months Ended			12 Months Ended
	Jun. 09, 2016	May 23, 2016	Mar. 29, 2016	May 18, 2015	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015	[1]
Class of Stock [Line Items]
Units issued in connection with private placement (in units)								5,402,985	765,307
Net proceeds from private equity placement								$ 0.0	$ 0.0	[1]	$ 297.4
Consideration for units issued in connection with private placement								$ 5.8	$ 9.8	[1]	$ 6.1
Aggregate percentage of interest								2.00%
Common Units
Class of Stock [Line Items]
Units issued in connection with private placement (in units)				7,692,308	5,200,000
Net proceeds from private equity placement				$ 297.4	$ 139.8
Gross proceed issuance of private placement offering				$ 300.0	$ 140.2
Common units per share (in units per share)				$ 39.00	$ 26.96
Placement fees				$ 2.6	$ 0.4
Consideration for units issued in connection with private placement				$ 6.1
General Partner
Class of Stock [Line Items]
Units issued in connection with private placement (in units)				156,986	106,122	1,938	15,307	108,060	15,307
Consideration for units issued in connection with private placement	$ 1.1		$ 8.2		$ 2.9	$ 0.1	$ 0.5
May 2016 Acquisition
Class of Stock [Line Items]
Consideration for units issued in connection with private placement		$ 7.1
Shell Pipeline Company L P | Common Units
Class of Stock [Line Items]
Units issued in connection with private placement (in units)								0	0
Shell Pipeline Company L P | General Partner
Class of Stock [Line Items]
Aggregate percentage of interest								2.00%
Shell Pipeline Company L P | May 2016 Acquisition | General Partner
Class of Stock [Line Items]
Aggregate percentage of interest								2.00%

[1] The financial information presented has been retrospectively adjusted for acquisitions of businesses under common control.