Earnings and Dividends per Share (Reconciliation of Denominator for Basic and Diluted Earnings Per Share) (Details) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings and Dividends Per Share [Abstract]
Weighted average common shares—basic	128,142,997	127,680,478	128,049,852	127,958,921
Weighted Average Number Diluted Shares Outstanding Adjustment	734,863	143,151	631,924	174,379
Weighted average common shares-diluted	128,877,860	127,823,629	128,681,776	128,133,300
Earnings per share attributable to Westlake Chemical Corporation: Basic (in dollars per share)	$ 4.06	$ 0.11	$ 5.94	$ 1.24
Earnings per share attributable to Westlake Chemical Corporation: Diluted (in dollars per share)	$ 4.04	$ 0.11	$ 5.91	$ 1.24