Earnings and Dividends per Share (Schedule of Net Income Attributable to Common Stockholders) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings and Dividends Per Share [Abstract]
Net income attributable to Westlake Chemical Corporation	$ 15	$ 119	$ 160	$ 191
Net income attributable to participating securities	(1)	(1)	(1)	(1)
Net income attributable to common shareholders	$ 14	$ 118	$ 159	$ 190