Partners' Capital (Cash Distributions) (Details) - USD ($) $ / shares in Units, $ in Millions														12 Months Ended
	Feb. 19, 2020	Nov. 19, 2019	Aug. 14, 2019	May 15, 2019	Feb. 14, 2019	Nov. 14, 2018	Aug. 15, 2018	May 15, 2018	Feb. 14, 2018	Nov. 14, 2017	Aug. 15, 2017	May 16, 2017	Feb. 21, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 25, 2018	[1]
Distribution Made To Limited Partner [Line Items]
Per Unit Distribution (in dollars per share)		$ 825.5000	$ 825.5000	$ 825.5000	$ 825.5000	$ 825.5000	$ 825.5000	$ 825.5000	$ 825.5000	$ 825.5000	$ 825.5000	$ 825.5000	$ 825.5000
Distribution Made to Limited Partner, Cash Distributions Paid		$ 68	$ 68	$ 68	$ 68	$ 68	$ 68	$ 68	$ 82	$ 82	$ 82	$ 82	$ 81	$ 353	$ 383	$ 431
General Partner [Member]
Distribution Made To Limited Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Paid		$ 18	$ 18	$ 18	$ 18	$ 18	$ 17	$ 18	$ 21	22	21	$ 21	$ 21
Subsequent Event [Member]
Distribution Made To Limited Partner [Line Items]
Per Unit Distribution (in dollars per share)	$ 825.5000
Distribution Made to Limited Partner, Cash Distributions Paid	$ 69
Subsequent Event [Member] | General Partner [Member]
Distribution Made To Limited Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Paid	$ 18
Series A Preferred Units
Distribution Made To Limited Partner [Line Items]
Preferred Unit, Quarterly Distribution										$ 7	$ 8						$ 10

[1] cash distribution paid on January 25, 2018 includes $8 million cash distribution for the three months ended December 31, 2017 and $2 million cash distribution for the period from January 1, 2018 through January 25, 2018.