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Description of Business and Significant Accounting Policies (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) plant	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Capitalized interest	$ 9	$ 7	$ 4
Provisional adjustment of income tax benefit			$ 591
Asset Retirement Obligation, Current	7	8
Asset Retirement Obligations, Noncurrent	$ 20	20
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)	77.20%
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
Accumulated Other Comprehensive Income (Loss) [Member] \| Accounting Standard Update 2018-02 [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax		$ 13