Earnings and Dividends per Share (Reconciliation of Denominator for Basic and Diluted Earnings Per Share) (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings and Dividends Per Share [Abstract]
Weighted average common shares—basic	127,701,340	128,216,105	127,872,434	128,408,841
Weighted Average Number Diluted Shares Outstanding Adjustment	252,567	336,255	200,632	362,103
Weighted average common shares-diluted	127,953,907	128,552,360	128,073,066	128,770,944
Earnings per share attributable to Westlake Chemical Corporation: Basic (in dollars per share)	$ 0.45	$ 1.22	$ 1.69	$ 2.70
Earnings per share attributable to Westlake Chemical Corporation: Diluted (in dollars per share)	$ 0.45	$ 1.22	$ 1.69	$ 2.69