Earnings and Dividends per Share (Schedule Of Net Income Attributable To Common Stockholders) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings and Dividends Per Share [Abstract]
Net income attributable to Westlake Chemical Corporation	$ 113	$ 57	$ 15	$ 145	$ 72	$ 158	$ 119	$ 72	$ 330	$ 421	$ 996
Net income attributable to participating securities									(1)	(2)	(5)
Net income attributable to common shareholders									$ 329	$ 419	$ 991