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Employee Benefits (Multiemployer Plans) (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2020 USD ($) plan | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Multiemployer Plans [Line Items] |  |  |
Number of multiemployer plans | plan | 2 |  |
Foreign Plan [Member] |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Plan Contribution | $ | $ 5 | $ 9 | $ 7

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- Definition Amount of contribution received by multiemployer pension plan from all employers participating in multiemployer pension plan determined to be individually significant. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 7 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450678-114947 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=35742348&loc=SL14450788-114948 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

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- Definition Number Of Multiemployer Plans + References No definition available. + Details
Name: | wlk_NumberOfMultiemployerPlans
Namespace Prefix: | wlk_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_RetirementPlanSponsorLocationAxis=us-gaap_ForeignPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |