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/presentationRef
-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=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-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=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-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=6876686&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

+ 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

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

+ Details

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

- Definition

Debt Instrument, Maturity

+ References

No definition available.

+ Details

Name:	wlk_DebtInstrumentMaturity
Namespace Prefix:	wlk_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Exchange Offer Percentage

+ References

No definition available.

+ Details

Name:	wlk_ExchangeOfferPercentage
Namespace Prefix:	wlk_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Long-Term Debt (Senior Notes Due 2021 and 2023) (Details) - USD ($) $ in Millions			1 Months Ended	12 Months Ended
	Feb. 15, 2018	Apr. 24, 2017	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 3,853	$ 3,678
Senior Notes [Member] \| 4.625% Westlake Senior Notes 2021 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 625	$ 625	625
Stated interest rate (percent)				4.625%
Debt instrument maturity				2021
Exchange Offer Percentage		100.00%
Senior Notes [Member] \| 4.875% Westlake Senior 2023 Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			434	$ 434	434
Stated interest rate (percent)				4.875%
Debt instrument maturity				2023
Exchange Offer Percentage		100.00%
Senior Notes [Member] \| 4.625% Subsidiary Senior Notes 2021 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 688	$ 63	63
Stated interest rate (percent)			4.625%	4.625%
Debt instrument maturity			2021	2021
Senior Notes [Member] \| 4.875% Subsidiary 2023 Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 450	$ 16	$ 16
Stated interest rate (percent)			4.875%	4.875%
Debt instrument maturity			2023	2023
Subsequent Event [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	102.313%