Related-Party Transactions Related-Party Transactions, Summary of Transactions Narrative (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Jun. 30, 2019 |
Mar. 31, 2019 |
Jun. 30, 2018 |
Jun. 30, 2019 |
Jun. 30, 2018 |
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| Recovery of Direct Costs | $ 7 | $ 3 | $ 10 | $ 10 | ||||||||||||||
| Revenues | 601 | 569 | [1],[2] | 1,231 | 1,115 | [1],[2] | ||||||||||||
| Related Party Transactions, Operating Expenses | [3] | 113 | 72 | [4] | 217 | 134 | [4] | |||||||||||
| Related Party Transactions, General and Administrative Expenses | $ 15 | $ 22 | [4] | $ 29 | $ 46 | [4] | ||||||||||||
| Concentration Risk, Percentage | 71.00% | 68.00% | 71.00% | 64.00% | ||||||||||||||
| Payments of Distributions to Affiliates | $ 294 | |||||||||||||||||
| Secondment and Logistics Services Agreement | ||||||||||||||||||
| Term Of Agreement | 10 years | |||||||||||||||||
| Length Of Time For Continuing Minimum Payments | 60 days | |||||||||||||||||
| Partner to Andeavor | Omnibus Agreement | ||||||||||||||||||
| Payment for Administrative Fees | $ 17 | |||||||||||||||||
| Andeavor to Partner | Secondment and Logistics Services Agreement | ||||||||||||||||||
| Long-term Purchase Commitment, Amount | $ 24 | $ 4 | 47 | $ 10 | ||||||||||||||
| Affiliated Entity | ||||||||||||||||||
| Revenues | [5] | $ 424 | $ 389 | [2],[4] | $ 868 | $ 716 | [2],[4] | |||||||||||
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