The number of limited partner units outstanding.

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The number of units sold in a private placement of each class of partners' capital account. Units represent shares of ownership of the general, limited, and preferred partners.

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The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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The cash outflow associated with the purchase of or advances to an equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Ownership interest purchased.

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Acquisitions and Divestitures - Additional Information (Details) - USD ($) $ in Millions	Feb. 28, 2019	Jan. 18, 2019	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Property, Plant and Equipment [Line Items]
Limited partner units			443,971,409	443,971,409
WES Operating [Member] \| Anadarko [Member] \| Common Units [Member]
Property, Plant and Equipment [Line Items]
Limited partner units					6,400,000
Mi Vida [Member]
Property, Plant and Equipment [Line Items]
Ownership percentage acquired	50.00%
Ranch Westex [Member]
Property, Plant and Equipment [Line Items]
Ownership percentage acquired	50.00%
Saddlehorn [Member]
Property, Plant and Equipment [Line Items]
Ownership percentage acquired	20.00%
Panola [Member]
Property, Plant and Equipment [Line Items]
Ownership percentage acquired	15.00%
Red Bluff Express [Member]
Property, Plant and Equipment [Line Items]
Ownership percentage acquired		30.00%
Acquisition, net investment		$ 92.5
Anadarko Midstream Assets [Member] \| WES Operating [Member] \| Common Units [Member]
Property, Plant and Equipment [Line Items]
Units issued	45,760,201
Anadarko Midstream Assets [Member] \| WES Operating [Member] \| Anadarko [Member] \| Common Units [Member]
Property, Plant and Equipment [Line Items]
Limited partner units	6,375,284
Anadarko [Member] \| Anadarko Midstream Assets [Member] \| WES Operating [Member]
Property, Plant and Equipment [Line Items]
Cash payment for acquisition	$ 2,000.0