Related-Party Transactions Related-Party Transactions, Summary of Affiliate Transactions (Details) - USD ($) $ / shares in Units, $ in Millions |
3 Months Ended | 9 Months Ended | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Nov. 14, 2017 |
Oct. 18, 2017 |
Sep. 30, 2017 |
Jun. 30, 2017 |
Mar. 31, 2017 |
Dec. 31, 2016 |
Sep. 30, 2016 |
Sep. 30, 2017 |
Sep. 30, 2016 |
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| Cost of Reimbursable Expense | $ 7 | $ 3 | $ 12 | $ 12 | ||||||||||
| Concentration Risk, Percentage | 49.00% | 60.00% | 49.00% | |||||||||||
| Cash Dividends Paid to Parent Company | $ 223 | |||||||||||||
| Distribution Made to Limited Partner, Distributions Declared, Per Unit | $ 0.9852 | [1],[2] | $ 0.9710 | $ 0.9400 | $ 0.9100 | |||||||||
| Distribution Made to Limited Partner, Distribution Date | Nov. 14, 2017 | Aug. 14, 2017 | May 15, 2017 | Feb. 14, 2017 | ||||||||||
| Subsequent Event | ||||||||||||||
| Distribution Made to Limited Partner, Declaration Date | Oct. 18, 2017 | |||||||||||||
| Distribution Made to Limited Partner, Cash Distributions Paid | $ 125 | |||||||||||||
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