The number of general partner units outstanding.

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=120397183&loc=d3e187171-122770

+ Details

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

- Definition

Percentage investment held by the managing member or general partner of the limited liability company (LLC) or limited partnership (LP).

+ References

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

- Definition

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

+ References

+ 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

+ Details

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

- Definition

Amount, before allowance for credit loss, of financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 79
-URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922352-210448

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919230-210447

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 80
-URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922355-210448

+ Details

Name:	us-gaap_NotesReceivableGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The number of units redeemed during the year 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=120397183&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=120397183&loc=d3e187171-122770

+ Details

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

- Definition

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

+ References

+ Details

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

- Definition

The cash outflow to reacquire common stock during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3291-108585

+ Details

Name:	us-gaap_PaymentsForRepurchaseOfCommonStock
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

Amount of stock repurchase plan authorized.

+ References

No definition available.

+ Details

Name:	us-gaap_StockRepurchaseProgramAuthorizedAmount1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount remaining of a stock repurchase plan authorized.

+ References

No definition available.

+ Details

Name:	us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Number of shares that have been repurchased and retired during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: 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=120397183&loc=d3e187085-122770

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644

+ Details

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

- Definition

The number of units sold as part of the over-allotment option of a public offering.

+ References

No definition available.

+ Details

Name:	wes_PartnersCapitalAccountUnitsSoldInPublicOfferingOverAllotment
Namespace Prefix:	wes_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage interest in the Anadarko Note Receivable transferred to an affiliate as part of a financial transaction.

+ References

No definition available.

+ Details

Name:	wes_PercentageInterestinAnadarkoNoteReceivableTransferredtoAffiliate
Namespace Prefix:	wes_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=srt_AffiliatedEntityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_PartnerTypeOfPartnersCapitalAccountAxis=us-gaap_LimitedPartnerMember
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:	dei_LegalEntityAxis=wes_WesternMidstreamOperatingLPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Equity and Partners' Capital - Additional Information (Details) - USD ($)		1 Months Ended	3 Months Ended
	Sep. 11, 2020	Mar. 31, 2021	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	May 31, 2008
Schedule of Investments [Line Items]
Common units outstanding		413,062,133	413,062,133		413,839,863
General partner units outstanding		9,060,641	9,060,641		9,060,641
Unit repurchases, authorized amount		$ 250,000,000.0	$ 250,000,000.0
Unit repurchases, number of units			1,115,808
Unit repurchases, amount			$ 16,241,000	$ 0
Unit repurchases, remaining authorized amount		$ 201,200,000	$ 201,200,000
WES [Member] \| Public [Member]
Schedule of Investments [Line Items]
Common units outstanding		210,280,555	210,280,555
Limited partner's interest			49.80%
Related Parties [Member]
Schedule of Investments [Line Items]
Anadarko note receivable						$ 260,000,000.0
Anadarko [Member]
Schedule of Investments [Line Items]
Anadarko note receivable - percentage interest transferred	98.00%
Anadarko note receivable	$ 260,000,000.0
WES [Member] \| WES Operating [Member]
Schedule of Investments [Line Items]
Limited partner's interest			98.00%
WES [Member] \| Related Parties [Member] \| Limited Partner [Member] \| WES [Member]
Schedule of Investments [Line Items]
Units redeemed from a related party	27,855,398
Occidental [Member]
Schedule of Investments [Line Items]
Units sold by a related party		11,500,000
Units sold to by a related party, over-allotment		1,500,000
Occidental [Member] \| WES [Member]
Schedule of Investments [Line Items]
Common units outstanding		202,781,578	202,781,578
Limited partner's interest			48.00%
General partner units outstanding		9,060,641	9,060,641
General partner's interest			2.20%
Occidental [Member] \| WES Operating [Member]
Schedule of Investments [Line Items]
Limited partner's interest			2.00%
WES Operating [Member]
Schedule of Investments [Line Items]
Common units outstanding		318,675,578	318,675,578		318,675,578