Long-Term Debt (Schedule of Long-term Debt) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Principal Amount	$ 3,626	$ 3,620
Unamortized Premium (Discount) and Debt Issuance Costs	(51)	(54)
Net, Long-term Debt	3,575	3,566
Long-term Debt, Current Maturities	(20)	0
Debt Instrument Unamortized Discount Premium and Debt Issuance Cost Net Excluding Current Maturities	(51)	(54)
Long term Debt Gross Excluding Current Maturities	3,606	3,620
Long-term Debt, net excluding Current Maturities	$ 3,555	3,566
Line of Credit \| 8.73% Senior Notes Due 2022
Debt Instrument [Line Items]
Stated interest rate (percent)	8.73%
Senior Notes \| 3.60% Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Principal Amount	$ 250	250
Unamortized Premium (Discount) and Debt Issuance Costs	0	(1)
Net, Long-term Debt	$ 250	249
Stated interest rate (percent)	3.60%
Senior Notes \| 3.6% Senior Notes Due 2026 [Member]
Debt Instrument [Line Items]
Principal Amount	$ 750	750
Unamortized Premium (Discount) and Debt Issuance Costs	(6)	(6)
Net, Long-term Debt	$ 744	744
Stated interest rate (percent)	3.60%
Senior Notes \| Loan related to tax-exempt waste disposal revenue bonds due 2027 [Member]
Debt Instrument [Line Items]
Principal Amount	$ 11	11
Unamortized Premium (Discount) and Debt Issuance Costs	0	0
Net, Long-term Debt	11	11
Senior Notes \| 1.625% Senior Notes Due 2029
Debt Instrument [Line Items]
Principal Amount	831	859
Unamortized Premium (Discount) and Debt Issuance Costs	(9)	(10)
Net, Long-term Debt	$ 822	849
Stated interest rate (percent)	1.625%
Senior Notes \| 3.375% Senior Notes Due 2030
Debt Instrument [Line Items]
Principal Amount	$ 300	300
Unamortized Premium (Discount) and Debt Issuance Costs	(4)	(4)
Net, Long-term Debt	$ 296	296
Stated interest rate (percent)	3.375%
Senior Notes \| 3.50% Senior Notes Due 2032 [Member]
Debt Instrument [Line Items]
Principal Amount	$ 250	250
Unamortized Premium (Discount) and Debt Issuance Costs	(1)	(1)
Net, Long-term Debt	$ 249	249
Stated interest rate (percent)	3.50%
Senior Notes \| 5.0% Senior Notes Due 2046 [Member]
Debt Instrument [Line Items]
Principal Amount	$ 700	700
Unamortized Premium (Discount) and Debt Issuance Costs	(22)	(23)
Net, Long-term Debt	$ 678	677
Stated interest rate (percent)	5.00%
Senior Notes \| 4.375% Senior Notes Due 2047 [Member]
Debt Instrument [Line Items]
Principal Amount	$ 500	500
Unamortized Premium (Discount) and Debt Issuance Costs	(9)	(9)
Net, Long-term Debt	$ 491	491
Stated interest rate (percent)	4.375%
Senior Notes \| 8.73% Senior Notes Due 2022
Debt Instrument [Line Items]
Principal Amount	$ 30	0
Unamortized Premium (Discount) and Debt Issuance Costs	0	0
Net, Long-term Debt	30	0
Debt Instrument Unamortized Discount Premium and debt issuance cost net Current Maturities	0	0
Long Term Debt Gross Current Maturities	$ (20)	0
Stated interest rate (percent)	8.73%
Senior Notes \| Term Loan Due Twenty Twenty Six
Debt Instrument [Line Items]
Principal Amount	$ 4	0
Unamortized Premium (Discount) and Debt Issuance Costs	0	0
Net, Long-term Debt	$ 4	$ 0
Stated interest rate (percent)	0.20%

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870

Reference 2: 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(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

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(22))
-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 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ 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 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

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

- Definition

Amount of unamortized debt discount (premium) and debt issuance costs.

+ References

+ Details

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

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870

Reference 2: 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(a)(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

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(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 4: 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(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ 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 210.5-02.19,20)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Definition

Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ 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 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Definition

Amount of unamortized debt discount (premium) and debt issuance costs, of long-term debt, classified as current.

+ References

No definition available.

+ Details

Name:	wlk_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostNetCurrentMaturities
Namespace Prefix:	wlk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Debt Instrument, Unamortized Discount (premium) and Debt Issuance Cost, Net, Excluding Current Maturities.

+ References

No definition available.

+ Details

Name:	wlk_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostNetExcludingCurrentMaturities
Namespace Prefix:	wlk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, before unamortized (discount) premium and debt issuance cost, of long-term debt, classified as current. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

No definition available.

+ Details

Name:	wlk_LongTermDebtGrossCurrentMaturities
Namespace Prefix:	wlk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but is not limited to, notes payable, bonds payable, commercial loans, convertible debt, subordinated debt and other types of debt. Excludes capital lease obligations

+ References

No definition available.

+ Details

Name:	wlk_LongTermDebtGrossExcludingCurrentMaturities
Namespace Prefix:	wlk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=wlk_EightPointSevenThreePercentSeniorNotesDueTwentyTwentyTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=wlk_ThreePointSixZeroPercentageSeniorNotesDueTwentyTwentyTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=wlk_ThreePointSixPercentSeniorNotesDueTwentyTwentySixMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=wlk_WasteDisposalRevenueBondsDueTwentyTwentySevenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=wlk_OnePointSixTwoFivePercentageSeniorNotesDueTwentyTwentyNineMemberDomain
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=wlk_ThreePointThreeSevenFiveSeniorNotesDueTwentyThirtyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=wlk_ThreePointFiveZeroPercentSeniorNotesDueTwentyThirtyTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=wlk_FivePercentSeniorNotesDueTwentyFortySixMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=wlk_FourPointThreeSevenFivePercentSeniorNotesDueTwentyFortySevenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=wlk_TermLoanDueTwentyTwentySixMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: