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Description of Business and Significant Accounting Policies (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) plant	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Oct. 01, 2018 USD ($)	Dec. 31, 2017 USD ($)
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Capitalized interest	$ 4	$ 9	$ 7
Asset Retirement Obligation, Current	12	7
Asset Retirement Obligations, Noncurrent	17	20
Stockholders' equity	$ 6,578	6,403	6,076		$ 5,369
Cumulative effect of accounting change
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Stockholders' equity					1
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
Limited Partner [Member] | IPO [Member] | Subsidiary of Common Parent [Member] | Westlake Chemical OpCo LP [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Limited partner interest (percent)	77.20%
Subsidiaries [Member] | Louisiana | Westlake Chemical OpCo LP [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of production facilities | plant	2
Subsidiaries [Member] | Kentucky | Westlake Chemical OpCo LP [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of production facilities | plant	1
Accumulated Other Comprehensive Income (Loss)
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Stockholders' equity	$ (64)	$ (74)	$ (62)		$ 7
Accumulated Other Comprehensive Income (Loss) | Accounting Standard Update 2018-02 [Member] | Cumulative effect of accounting change
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Stockholders' equity				$ 13

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