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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings and Dividends Per Share [Abstract]
Weighted average common shares—basic	128,060,193	127,701,340	128,053,337	127,872,434
Weighted Average Number Diluted Shares Outstanding Adjustment	705,621	252,567	656,760	200,632
Weighted average common shares-diluted	128,765,814	127,953,907	128,710,097	128,073,066
Earnings per share attributable to Westlake Chemical Corporation: Basic (in dollars per share)	$ 4.71	$ 0.45	$ 10.65	$ 1.69
Earnings per share attributable to Westlake Chemical Corporation: Diluted (in dollars per share)	$ 4.69	$ 0.45	$ 10.60	$ 1.69