Earnings and Dividends per Share (Schedule of Net Income Attributable to Common Stockholders) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings and Dividends Per Share [Abstract]
Net income attributable to Westlake Chemical Corporation	$ 57	$ 158	$ 217	$ 349
Net income attributable to participating securities	0	(1)	(1)	(2)
Net income attributable to common shareholders	$ 57	$ 157	$ 216	$ 347