(Deficit) Equity - Public Offerings (Details) - USD ($) $ / shares in Units, $ in Millions						1 Months Ended	3 Months Ended			12 Months Ended
	Feb. 06, 2018	Sep. 15, 2017	Jun. 09, 2016	May 23, 2016	Mar. 29, 2016	Nov. 30, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Consideration for units issued in connection with private placement										$ 20.0	$ 5.8	$ 9.8
Aggregate percentage of interest											200.00%
Units issued in connection with private placement (in units)											5,402,985
Units issued in connection with public offering (in units)										36,764,707	5,275,510
Net proceeds from public offerings										$ 973.3	$ 277.9	818.1
Contributions from general partner		$ 2.8								20.0	5.8	16.9
Net proceeds from equity offerings										$ 973.3	$ 277.9	818.1
May 2016 Acquisition
Class of Stock [Line Items]
Consideration for units issued in connection with private placement				$ 7.1
Common Units
Class of Stock [Line Items]
Placement fees							$ 0.4
Units issued in connection with private placement (in units)						1,000,000,000.00	5,200,000
Gross proceed issuance of private placement offering							$ 140.2
Common units per share (in units per share)							$ 26.96
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]
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
Units issued in connection with private placement (in units)								94,925	750,000		5,294,925
Gross proceed issuance of private placement offering								$ 3.0	$ 25.5
Units issued in connection with public offering (in units)		5,170,000		1,575,000	12,650,000					25,000,000	5,170,000
Net proceeds from public offerings		$ 135.1	$ 51.8		$ 395.1
Common units per share (in units per share)			$ 33.25	$ 33.25	$ 31.75			$ 31.51	$ 34.00
Common Units | Shell Pipeline Company L P
Class of Stock [Line Items]
Units issued in connection with private placement (in units)											0
Units issued in connection with public offering (in units)										11,029,412	0
General Partner
Class of Stock [Line Items]
Consideration for units issued in connection with private placement			$ 1.1		$ 8.2		$ 2.9		$ 0.5
Units issued in connection with private placement (in units)							106,122	1,938	15,307		108,060
Units issued in connection with public offering (in units)		105,510	32,143		258,163					735,295	105,510
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										$ 20.0	$ 5.8	$ 16.9
General Partner | Shell Pipeline Company L P | May 2016 Acquisition
Class of Stock [Line Items]
Aggregate percentage of interest										2.00%
Private Placement | Common Units
Class of Stock [Line Items]
Sale of stock, price per share (in dollars per share)	$ 27.20
Units issued in connection with private placement (in units)	11,029,412
Gross proceed issuance of private placement offering	$ 300.0
Private Placement | General Partner
Class of Stock [Line Items]
Consideration for units issued in connection with private placement	$ 6.1
Units issued in connection with private placement (in units)	225,091
IPO | Common Units
Class of Stock [Line Items]
Sale of common units (in units)	25,000,000
Net proceeds from public offering	$ 673.3
Gross proceeds from public offering	$ 680.0
Sale of stock, price per share (in dollars per share)	$ 27.20
Underwriter fees	$ 6.0
Placement fees	0.7
IPO | General Partner
Class of Stock [Line Items]
Consideration for units issued in connection with private placement	$ 13.9
Units issued in connection with public offering (in units)	510,204