v3.7.0.1
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.