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Earnings and Dividends per Share (Reconciliation of Denominator for Basic and Diluted Earnings Per Share) (Details) - $ / shares
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Earnings and Dividends Per Share [Abstract]    
Weighted average common shares—basic 127,955,532 128,237,364
Weighted Average Number Diluted Shares Outstanding Adjustment 527,841 205,608
Weighted average common shares-diluted 128,483,373 128,442,972
Earnings per share attributable to Westlake Chemical Corporation: Basic (in dollars per share) $ 1.88 $ 1.13
Earnings per share attributable to Westlake Chemical Corporation: Diluted (in dollars per share) $ 1.87 $ 1.13