(Deficit) Equity - Public Offerings (Details) - USD ($) $ / shares in Units, $ in Millions								3 Months Ended			12 Months Ended
		Sep. 15, 2017	Jun. 09, 2016	May 23, 2016	Mar. 29, 2016	Nov. 17, 2015	May 18, 2015	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Class of Stock [Line Items]
Units issued in connection with public offering (in units)											5,275,510		25,229,591
Net proceeds from public offerings	[1]										$ 277.9		$ 818.1		$ 296.8
Contributions from general partner		$ 2.8									$ 5.8	[1]	16.9	[1]	6.1	[1]
Aggregate percentage of interest											2.00%
Consideration for units issued in connection with private placement											$ 5.8		9.8	[2]	6.1	[2]
Net proceeds from public offerings											$ 277.9		$ 818.1	[2]	296.8	[2]
May 2016 Acquisition
Class of Stock [Line Items]
Consideration for units issued in connection with private placement				$ 7.1
364 Day Revolver
Class of Stock [Line Items]
Debt instrument term											364 days
Five Year Revolver due October 2019
Class of Stock [Line Items]
Debt instrument term											5 years
Shell Treasury Center West Inc | Five Year Revolver
Class of Stock [Line Items]
Debt instrument term		5 years						5 years			5 years
Shell Treasury Center West Inc | 364 Day Revolver
Class of Stock [Line Items]
Debt instrument term					364 days						364 days
Shell Treasury Center West Inc | Five Year Revolver due October 2019
Class of Stock [Line Items]
Debt instrument term											5 years
Common Units
Class of Stock [Line Items]
Units issued in connection with public offering (in units)						9,200,000
Common units per share (in units per share)							$ 39.00	$ 26.96
Gross proceeds from public offering						$ 299.4
Underwriter fees						2.6
Placement fees							$ 2.6	$ 0.4
Consideration for units issued in connection with private placement							$ 6.1
Net proceeds from public offerings						$ 296.8
Common Units | May 2016 Acquisition
Class of Stock [Line Items]
Units issued in connection with public offering (in units)				10,500,000
Net proceeds from public offerings				$ 345.8
Common Units | General Public
Class of Stock [Line Items]
Units issued in connection with public offering (in units)		5,170,000		1,575,000	12,650,000						5,170,000		24,725,000
Net proceeds from public offerings		$ 135.1	$ 51.8		$ 395.1
Common units per share (in units per share)		$ 26.14	$ 33.25	$ 33.25	$ 31.75				$ 31.51	$ 34.00
Gross proceeds from public offering			$ 52.4	$ 349.1	$ 401.6
Underwriter fees			0.5	2.9	6.3
Placement fees			$ 0.1	$ 0.4	$ 0.2				$ 0.1	$ 0.1
Common Units | Shell Pipeline Company L P
Class of Stock [Line Items]
Units issued in connection with public offering (in units)											0		0
General Partner
Class of Stock [Line Items]
Units issued in connection with public offering (in units)		105,510	32,143		258,163	187,755					105,510		504,591
Consideration for units issued in connection with private placement			$ 1.1		$ 8.2			$ 2.9	$ 0.1	$ 0.5
General Partner | May 2016 Acquisition
Class of Stock [Line Items]
Units issued in connection with public offering (in units)				214,285
General Partner | Shell Pipeline Company L P
Class of Stock [Line Items]
Net proceeds from public offerings											$ 0.0
Contributions from general partner											$ 5.8		$ 16.9		$ 6.1
Aggregate percentage of interest											2.00%
General Partner | Shell Pipeline Company L P | May 2016 Acquisition
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.

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