Major Customers and Concentration of Credit Risk (Details) - First Major Customer - MPC		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues And Other Income]
Concentration Risk [Line Items]
Concentration risk, percentage	[1]	54.00%	48.00%	36.00%
Revenue Benchmark [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	[1],[2]	56.00%	50.00%	37.00%
Logistics and Storage [Member] | Revenues And Other Income]
Concentration Risk [Line Items]
Concentration risk, percentage	[1]	88.00%	90.00%	90.00%
Logistics and Storage [Member] | Revenue Benchmark [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	[1],[2]	91.00%	94.00%	92.00%
Gathering and Processing [Member] | Revenues And Other Income]
Concentration Risk [Line Items]
Concentration risk, percentage	[1]	4.00%	2.00%	0.00%
Gathering and Processing [Member] | Revenue Benchmark [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	[1],[2]	4.00%	3.00%	0.00%

[1] The percent calculations exclude revenues attributable to volumes shipped by MPC under joint tariffs with third parties, which are treated as third-party revenue for accounting purposes.

[2] Operating revenues consist of service revenue, service revenue - product related, rental income and product sales.