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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income attributable to Westlake Chemical Corporation	$ 308	$ 211	$ 873	$ 502
Net income attributable to participating securities	(1)	(1)	(4)	(3)
Net income attributable to common shareholders	$ 307	$ 210	$ 869	$ 499