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Equity (Deficit) (Details) - USD ($)			3 Months Ended		9 Months Ended
Equity (Deficit) (Details) - USD ($)	Feb. 06, 2018	Mar. 02, 2016	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2018	Dec. 31, 2018
Class of Stock [Line Items]
Aggregate percentage of general partner interest					2.00%
Issuance of common units, maximum proceeds		$ 300,000,000
Net proceeds from equity offerings				$ 973,000,000
Contribution from general partner for additional shares issued	$ 14,000,000
Net proceeds from equity offerings			$ 0	973,000,000
Consideration for units issued to our general partner			$ 0	20,000,000
Common unitholders' capital account, units outstanding (in shares)			223,811,781
Ownership interest percentage			43.80%
Five Year Fixed Facility
Class of Stock [Line Items]
Repayments of debt			$ 247,000,000
Debt instrument term			5 years
Five Year Revolver due December 2022
Class of Stock [Line Items]
Repayments of debt			$ 726,000,000
Debt instrument term			5 years
General Partner
Class of Stock [Line Items]
Aggregate percentage of general partner interest			2.00%
Units issued in connection with public offering (in shares)	510,204
Units issued under the ATM Program (in shares)	225,091
Capital units, publicly owned (in shares)			4,567,588
Common Units
Class of Stock [Line Items]
Common units per share (in USD per share)	$ 27.20
Units issued under the ATM Program (in shares)	11,029,412
Net proceeds from equity offerings	$ 300,000,000
Consideration for units issued to our general partner	$ 6,000,000
Shell Pipeline Company L P \| General Partner
Class of Stock [Line Items]
Aggregate percentage of general partner interest	2.00%		2.00%
Shell Pipeline Company L P \| Limited Partner
Class of Stock [Line Items]
Aggregate percentage of general partner interest			98.00%
Shell Pipeline Company L P \| Common Units
Class of Stock [Line Items]
Common unitholders' capital account, units outstanding (in shares)			99,979,548			99,979,548
General Public \| Common Units
Class of Stock [Line Items]
Units issued in connection with public offering (in shares)	25,000,000
Net proceeds from equity offerings	$ 673,000,000
Gross proceeds from public offering	$ 680,000,000
Common units per share (in USD per share)	$ 27.20
Underwriter fees	$ 6,000,000
Transaction fees	$ 1,000,000
Common unitholders' capital account, units outstanding (in shares)			123,832,233			123,832,233
Capital units, publicly owned (in shares)			123,832,233
Zydeco
Class of Stock [Line Items]
Distributions to noncontrolling interest			$ 1,000,000	0
Odyssey
Class of Stock [Line Items]
Distributions to noncontrolling interest			$ 2,000,000	$ 2,000,000