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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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