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Equity (Cash Distributions) (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended								12 Months Ended
		Jan. 25, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distributions to preferred units											$ 2,060	$ 1,288	$ 938
Subsequent Event
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution made to limited partner, declaration date		Jan. 25, 2019
Distributions to preferred units		$ 514
Cash distributions declared per limited partner common unit		$ 0.6475
Distribution made to limited partner, distribution date		Feb. 14, 2019
Distribution made to limited partner, date of record		Feb. 05, 2019
Limited Partners Common Units
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distributions to preferred units	[1]										$ 1,985	$ 895	$ 692
Cash distributions declared per limited partner common unit			$ 0.6475	$ 0.6375	$ 0.6275	$ 0.6175	$ 0.6075	$ 0.5875	$ 0.5625	$ 0.5400	$ 2.5300	$ 2.2975
[1] See Note 8 for distribution information.

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