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Description of Business and Significant Accounting Policies (Narrative) (Details) $ / shares in Units, $ in Millions		12 Months Ended
	Aug. 04, 2014	Dec. 31, 2018 USD ($) plant	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Aug. 31, 2016 $ / shares
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Capitalized interest		$ 7	$ 4	$ 10
Provisional adjustment of income tax benefit			591
Asset Retirement Obligation, Current		8	3
Asset Retirement Obligations, Noncurrent		20	18
Net Cash Provided by (Used in) Financing Activities		(1,427)	6	1,687
Net Cash Provided by (Used in) Operating Activities		$ 1,409	1,528	867
Minimum [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Deferred Cost, Amortization Period		3 years
Maximum [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Deferred Cost, Amortization Period		6 years
Westlake Chemical OpCo LP [Member] \| Limited Partner [Member] \| IPO [Member] \| Subsidiary of Common Parent [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Limited partner interest (percent)	89.40%	81.70%
Westlake Chemical OpCo LP [Member] \| Subsidiaries [Member] \| Louisiana
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of production facilities \| plant		2
Westlake Chemical OpCo LP [Member] \| Subsidiaries [Member] \| Kentucky
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of production facilities \| plant		1
Axiall Corporation [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Share price (in dollars per share) \| $ / shares					$ 33.00
Accounting Standards Update 2016-18 [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Net Cash Provided by (Used in) Financing Activities			160	1,533
Net Cash Provided by (Used in) Operating Activities			$ 1,538	$ 834