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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings and Dividends Per Share [Abstract]
Weighted average common shares—basic	127,680,478	128,485,182	127,958,921	128,506,712
Weighted Average Number Diluted Shares Outstanding Adjustment	143,151	365,153	174,379	375,240
Weighted average common shares-diluted	127,823,629	128,850,335	128,133,300	128,881,952
Earnings per share attributable to Westlake Chemical Corporation: Basic (in dollars per share)	$ 0.11	$ 0.92	$ 1.24	$ 1.48
Earnings per share attributable to Westlake Chemical Corporation: Diluted (in dollars per share)	$ 0.11	$ 0.92	$ 1.24	$ 1.47