Amount for accounts payable to related parties.

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

- Definition

Amount of receivables arising from transactions with related parties due within one year or the normal operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(k)(1))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

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 210.5-02.3(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39622-107864

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39603-107864

+ Details

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

- Definition

Amount of payable due to an entity that is affiliated with the reporting entity by means of direct or indirect ownership.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-04.12(3))
-URI http://asc.fasb.org/extlink&oid=6488278&loc=d3e603758-122996

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.15(3))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(k)(1))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.17)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 852
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6918054&loc=d3e56071-112765

+ Details

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

- Definition

Amount of distribution received from equity method investee for return on investment, classified as operating activities. Excludes distribution for return of investment, classified as investing activities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(10))
-URI http://asc.fasb.org/extlink&oid=114873790&loc=SL114874131-224263

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(12))
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 21D
-URI http://asc.fasb.org/extlink&oid=109223946&loc=SL94080555-108585

+ Details

Name:	us-gaap_EquityMethodInvestmentDividendsOrDistributions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

+ Details

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of financial support to be provided in future by investment company to investee.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 20
-Section 50
-Paragraph 16
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66023616&loc=SL35737436-115832

+ Details

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

- Definition

Amount of investment in equity method investee and investment in and advance to affiliate.

+ 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 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

+ References

No definition available.

+ Details

Name:	us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The cash outflow associated with extending a long-term loan to a related party. Alternate caption: Payments for Advances to Affiliates.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3213-108585

+ Details

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

- Definition

Purchases during the period (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ References

No definition available.

+ Details

Name:	us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07.1(c))
-URI http://asc.fasb.org/extlink&oid=114873854&loc=SL114874292-224272

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(e))
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

+ Details

Name:	us-gaap_RevenueFromRelatedParties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Equity Method Investment, Ownership Percentage, Option

+ References

No definition available.

+ Details

Name:	wlk_EquityMethodInvestmentOwnershipPercentageOption
Namespace Prefix:	wlk_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Lease expense incurred for office space.

+ References

No definition available.

+ Details

Name:	wlk_OfficeLeaseExpense
Namespace Prefix:	wlk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Payments made for purchases and lease expenses.

+ References

No definition available.

+ Details

Name:	wlk_PurchasesAndLeaseExpense
Namespace Prefix:	wlk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Related Party Transaction, Plant Capacity

+ References

No definition available.

+ Details

Name:	wlk_RelatedPartyTransactionPlantCapacity
Namespace Prefix:	wlk_
Data Type:	num:massItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=wlk_PipelineFeesForTransportOfNaturalGasLiquidFeedstocksMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=wlk_CypressInterstatePipelineLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	srt_CounterpartyNameAxis=wlk_CypressInterstatePipelineLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=wlk_InfraServKnapsackGmbHCo.KGMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=wlk_InfraServGendorfGmbHCo.KGMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=wlk_InfraServKnapsackGendorfGmbHCo.KGMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=wlk_ElectricityAndTechnicalServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=wlk_RSCogenLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=wlk_VinylSolutionsLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=wlk_LACCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=wlk_AmericanAirLiquideHoldingsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

Related Party and Affiliate Transactions (Details) $ in Millions, lb in Billions		4 Months Ended	12 Months Ended
	Jun. 17, 2015 USD ($) lb	Dec. 31, 2016 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Feb. 01, 2018	Jan. 31, 2018
Related Party Transaction [Line Items]
Related party receivable			$ 6	$ 9
Dividends received from equity method investments			5	6	$ 5
Affiliates [Member]
Related Party Transaction [Line Items]
Incurred and paid lease payments			3	3	3
Pipeline Fees For Transport Of Natural Gas Liquid Feedstocks [Member] \| Cypress Interstate Pipeline L.L.C [Member] \| Corporate Joint Venture [Member]
Related Party Transaction [Line Items]
Purchases from related parties			14	15	14
Accounts payable due to affiliate			$ 2	1
Cypress Interstate Pipeline L.L.C [Member] \| Corporate Joint Venture [Member]
Related Party Transaction [Line Items]
Ownership interest (in percent)			50.00%
Investments in joint ventures			$ 8	9
InfraServ Knapsack GmbH & Co. KG [Member] \| Affiliates [Member]
Related Party Transaction [Line Items]
Ownership percentage by parent						5.00%	15.00%
InfraServ Gendorf GmbH & Co. KG [Member] \| Affiliates [Member]
Related Party Transaction [Line Items]
Ownership percentage by parent						9.00%	11.00%
InfraServ Knapsack & Gendorf GmbH & Co. KG [Member] \| Affiliates [Member]
Related Party Transaction [Line Items]
Investments in joint ventures			57	46
InfraServ Knapsack & Gendorf GmbH & Co. KG [Member] \| Electricity And Technical Services [Member] \| Affiliates [Member]
Related Party Transaction [Line Items]
Purchases from related parties			145	133	131
Accounts payable due to affiliate			$ 48	33
RS Cogen LLC [Member] \| Affiliates [Member]
Related Party Transaction [Line Items]
Ownership interest (in percent)			50.00%
Investments in joint ventures			$ 5	10
Purchases from related parties		$ 9	$ 25	26
Vinyl Solutions, LLC [Member] \| Affiliates [Member]
Related Party Transaction [Line Items]
Ownership interest (in percent)			50.00%
Sales to related parties		6	$ 13	17
Related party receivable			3	7
LACC [Member] \| Affiliates [Member]
Related Party Transaction [Line Items]
Ownership interest (in percent)	10.00%
Investments in joint ventures			183	125
Related party receivable			1	0
Plant capacity (in lbs) \| lb	2
Maximum Capital Commitment	$ 225
Optional ownership percentage	50.00%
Funding to related parties		$ 17	58	66
American Air Liquide Holdings [Member] \| American Air Liquide Holdings, Inc. [Member]
Related Party Transaction [Line Items]
Sales to related parties			7	7	4
Related party receivable			1	1
Accounts payable due to related parties			4	2
Purchases and lease expense to related parties			$ 31	$ 30	$ 22