Related-Party Transactions Related-Party Transactions, Summary of Affiliate Transactions (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended					6 Months Ended			12 Months Ended
	Aug. 14, 2017	Jul. 19, 2017	Jun. 30, 2017		Mar. 31, 2017		Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016		Dec. 31, 2016
Volume Gains (Losses) Value			$ 2.0				$ 2.0	$ 5.0	$ 3.0
Distribution Made to Limited Partner, Distributions Declared, Per Unit			$ 0.971	[1],[2]	$ 0.94	[1]					$ 0.91
Distribution Made to Limited Partner, Distribution Date					May 15, 2017						Feb. 14, 2017
Distribution Made to Limited Partner, Cash Distributions Paid								195.0	149.0	[3]
Cost of Reimbursable Expense			$ 3.0				3.0	5.0	9.0
Cash Dividends Paid to Parent Company								(148.0)
Subsequent Event
Distribution Made to Limited Partner, Declaration Date		Jul. 19, 2017
Distribution Made to Limited Partner, Distribution Date	Aug. 14, 2017
Distribution Made to Limited Partner, Cash Distributions Paid	$ 75.0
North Dakota Gathering and Processing Assets [Member]
managing member or general partner, subsequent distribution amount forfeited								12.5
Secondment and Logistics Services Agreement | Andeavor to Partner
Long-term Purchase Commitment, Amount			$ 5.0				$ 1.0	$ 10.0	$ 6.0

[1] This distribution is net of $12.5 million of IDRs waived by TLGP for each of the three months ended June 30, 2017 and March 31, 2017.

[2] This distribution was declared on July 19, 2017 and will be paid on the date of distribution.

[3] (a)Adjusted to include the historical results of the Predecessors. See Note 1 for further discussion.