Description of Business and Basis of Presentation (Details) - segment	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018
Description Of Business And Basis Of Presentation [Line Items]
Number of reportable segments	1
Pecten Midstream LLC (“Pecten”)
Description Of Business And Basis Of Presentation [Line Items]
SHLX Ownership	100.00%
Shell’s Retained Ownership	0.00%
Sand Dollar Pipeline LLC (“Sand Dollar”)
Description Of Business And Basis Of Presentation [Line Items]
SHLX Ownership	100.00%
Shell’s Retained Ownership	0.00%
Triton West LLC (“Triton”)
Description Of Business And Basis Of Presentation [Line Items]
SHLX Ownership	100.00%
Shell’s Retained Ownership	0.00%
Zydeco Pipeline Company LLC (“Zydeco”)
Description Of Business And Basis Of Presentation [Line Items]
SHLX Ownership	92.50%
Shell’s Retained Ownership	7.50%
Amberjack Pipeline Company LLC (“Amberjack”) - Series A
Description Of Business And Basis Of Presentation [Line Items]
SHLX Ownership	75.00%	75.00%
Shell’s Retained Ownership	0.00%
Amberjack Pipeline Company LLC (“Amberjack”) - Series B
Description Of Business And Basis Of Presentation [Line Items]
SHLX Ownership	50.00%	50.00%
Shell’s Retained Ownership			0.00%
Mars Oil Pipeline Company LLC (“Mars”)
Description Of Business And Basis Of Presentation [Line Items]
SHLX Ownership	71.50%	71.50%
Shell’s Retained Ownership	0.00%
Odyssey Pipeline L.L.C. (“Odyssey”)
Description Of Business And Basis Of Presentation [Line Items]
SHLX Ownership	71.00%
Shell’s Retained Ownership	0.00%
Bengal Pipeline Company LLC (“Bengal”)
Description Of Business And Basis Of Presentation [Line Items]
SHLX Ownership	50.00%	50.00%
Shell’s Retained Ownership	0.00%
Crestwood Permian Basin LLC (“Permian Basin”)
Description Of Business And Basis Of Presentation [Line Items]
SHLX Ownership	50.00%	50.00%
Shell’s Retained Ownership	0.00%
LOCAP LLC (“LOCAP”)
Description Of Business And Basis Of Presentation [Line Items]
SHLX Ownership	41.48%	41.48%
Shell’s Retained Ownership	0.00%
Poseidon Oil Pipeline Company LLC (“Poseidon”)
Description Of Business And Basis Of Presentation [Line Items]
SHLX Ownership	36.00%	36.00%
Shell’s Retained Ownership	0.00%
Explorer Pipeline Company (“Explorer”)
Description Of Business And Basis Of Presentation [Line Items]
SHLX Ownership	12.62%
Shell’s Retained Ownership	25.97%
Proteus Oil Pipeline Company, LLC (“Proteus”)
Description Of Business And Basis Of Presentation [Line Items]
SHLX Ownership	10.00%	10.00%
Shell’s Retained Ownership	0.00%
Endymion Oil Pipeline Company, LLC (“Endymion”)
Description Of Business And Basis Of Presentation [Line Items]
SHLX Ownership	10.00%	10.00%
Shell’s Retained Ownership	0.00%
Colonial Pipeline Company (“Colonial”)
Description Of Business And Basis Of Presentation [Line Items]
SHLX Ownership	6.00%
Shell’s Retained Ownership	10.12%
Cleopatra Gas Gathering Company, LLC (“Cleopatra”)
Description Of Business And Basis Of Presentation [Line Items]
SHLX Ownership	1.00%
Shell’s Retained Ownership	0.00%