Earnings per Share (Schedule of Net Income Attributable to Common Stockholders) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income attributable to Westlake Chemical Corporation	$ 278	$ 153	$ 565	$ 291
Net income attributable to participating securities	(2)	(1)	(3)	(2)
Net income attributable to common shareholders	$ 276	$ 152	$ 562	$ 289