Related Party Transactions - Additional Information (Details)		3 Months Ended			12 Months Ended
	Nov. 03, 2014 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) credit_facility	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Related Party Transaction [Line Items]
Statute of limitations expirations, number of days						60 days
Number of days within combined tax filing submission						15 days
Other contributions from Parent						$ 13,400,000	$ 17,100,000	$ 9,700,000
Gain (loss) from sale of excess allowance oil						3,200,000	1,300,000	1,300,000
Pension and Retirement Savings Plans
Related Party Transaction [Line Items]
Pension and postretirement health and life insurance						6,300,000	4,300,000	5,100,000
Defined benefit plan costs						2,500,000	1,700,000	2,000,000.0
Management Agreement
Related Party Transaction [Line Items]
General and administrative expense						8,500,000	8,100,000	7,700,000
Omnibus Agreement
Related Party Transaction [Line Items]
General and administrative expense						$ 8,500,000	8,500,000	8,500,000
Shell Treasury Center West Inc
Related Party Transaction [Line Items]
Number of revolving credit facilities | credit_facility						4
SPLC
Related Party Transaction [Line Items]
General insurance expense						$ 15,200,000	8,000,000.0	5,900,000
Operations and maintenance costs allocated from parent						15,100,000	17,100,000	15,900,000
General and administrative costs allocated from parent						32,900,000	26,300,000	24,000,000.0
SPLC | Reimbursement for Maintenance Expense and Capital Expenditures
Related Party Transaction [Line Items]
Other contributions from Parent						0	0	1,600,000
Shell Pipeline Company L P
Related Party Transaction [Line Items]
Reimbursements related to costs and expenses for maintenance projects						$ 11,400,000	$ 16,100,000	$ 3,000,000.0
Shell Pipeline Company L P
Related Party Transaction [Line Items]
Payment of general and administrative fee	$ 8,500,000
Zydeco Pipeline Company LLC (“Zydeco”)
Related Party Transaction [Line Items]
Noncontrolling interest						7.50%	7.50%	7.50%
Odyssey Pipeline L.L.C.
Related Party Transaction [Line Items]
Noncontrolling interest						29.00%	29.00%	29.00%
Lockport | Shell Pipeline Company L P
Related Party Transaction [Line Items]
Reimbursements related to costs and expenses for maintenance projects						$ 1,700,000	$ 1,600,000
Zydeco Pipeline Company LLC (“Zydeco”) | Shell Pipeline Company L P
Related Party Transaction [Line Items]
Reimbursements related to costs and expenses for maintenance projects						$ 11,400,000	$ 14,400,000	$ 1,400,000
Scenario, Forecast | SPLC | Second Amendment
Related Party Transaction [Line Items]
Distribution to holders of incentive distribution rights waived		$ 16,000,000.0	$ 17,000,000.0	$ 17,000,000.0	$ 50,000,000.0