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
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

[1] (a)Represents cash distributions declared and paid during the nine months ended September 30, 2017, relating to the fourth quarter of 2016 through the second quarter of 2017.

[2] (b)See reconciliation of general partner and limited partner’s earnings to amounts recorded to equity for the periods presented.