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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings and Dividends Per Share [Abstract]
Net income attributable to Westlake Chemical Corporation	$ 72	$ 158	$ 119	$ 72	$ 123	$ 308	$ 278	$ 287	$ 421	$ 996	$ 1,304
Net income attributable to participating securities									(2)	(5)	(7)
Net income attributable to common shareholders									$ 419	$ 991	$ 1,297