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Description Of Business And Significant Accounting Policies (Narrative) (Details) $ / shares in Units, $ in Millions			3 Months Ended	12 Months Ended
	Sep. 29, 2017	Aug. 04, 2014	Sep. 30, 2016 USD ($)	Dec. 31, 2017 USD ($) plant	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Aug. 31, 2016 USD ($) $ / shares
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Provisional adjustment of income tax benefit				$ 591
Aggregate principal amount of senior notes			$ 1,450
Capitalized interest				4	$ 10	$ 10
Asset Retirement Obligation, Current				3	4
Asset Retirement Obligations, Noncurrent				$ 18	$ 17
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)	81.70%	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
Revolving Credit Facility [Member] \| Senior Secured Revolving Credit Facility [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Maximum borrowing capacity				$ 1,000			$ 1,000
Axiall Corporation [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Share price (in dollars per share) \| $ / shares							$ 33.00