Percentage investment held by members or limited partners of limited liability company (LLC) or limited partnership (LP).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

+ Details

Name:	us-gaap_LimitedLiabilityCompanyLLCOrLimitedPartnershipLPMembersOrLimitedPartnersOwnershipInterest
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of limited partner units outstanding.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 5
-Subparagraph (SAB Topic 4.F)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187171-122770

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70434-108055

+ Details

Name:	us-gaap_LimitedPartnersCapitalAccountUnitsOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 5
-Subparagraph (SAB Topic 4.F)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187171-122770

+ Details

Name:	us-gaap_PartnersCapitalAccountUnitsSoldInPrivatePlacement
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

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.

+ References

No definition available.

+ Details

Name:	us-gaap_ScheduleOfInvestmentsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of common units issued for each convertible Class C unit that is converted.

+ References

No definition available.

+ Details

Name:	wes_ConvertibleUnitsUnitsIssuedUponConversion
Namespace Prefix:	wes_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Total change in each class of partners' capital accounts due to the beneficial conversion feature.

+ References

No definition available.

+ Details

Name:	wes_PartnersCapitalAccountBeneficialConversionFeature
Namespace Prefix:	wes_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_CapitalUnitsByClassAxis=wes_ClassCUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=wes_WesternMidstreamPartnersLPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	wes_OwnershipInterestByPartyAxis=wes_PublicMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=wes_OccidentalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=wes_WesternMidstreamOperatingLPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=wes_WesternMidstreamPartnersLPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=wes_WesternMidstreamOperatingLPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=wes_OtherSubsidiariesOfAnadarkoMember
Namespace Prefix:
Data Type:	na
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Period Type:

Equity and Partners' Capital - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended	12 Months Ended
	Nov. 30, 2014	Sep. 30, 2019	Dec. 31, 2014	Feb. 28, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Limited partner units		453,032,050			218,937,797
Class C Units [Member]
Schedule of Investments [Line Items]
Beneficial conversion feature			$ 34.8
WES [Member] \| Public [Member]
Schedule of Investments [Line Items]
Limited partner units		201,834,433
Ownership interest		44.60%
Occidental [Member] \| WES [Member]
Schedule of Investments [Line Items]
Limited partner units		251,197,617
Ownership interest		55.40%
Occidental [Member] \| WES Operating [Member]
Schedule of Investments [Line Items]
Ownership interest		2.00%
WES [Member] \| WES Operating [Member]
Schedule of Investments [Line Items]
Ownership interest		98.00%
WES Operating [Member]
Schedule of Investments [Line Items]
Units issued		308,723
WES Operating [Member] \| Class C Units [Member]
Schedule of Investments [Line Items]
Limited partner units				14,681,388
Units issued		308,723
Class C units, common units issued upon conversion				1
WES Operating [Member] \| Class C Units [Member] \| Other Subsidiaries of Anadarko [Member]
Schedule of Investments [Line Items]
Units issued	10,913,853