Accumulated Other Comprehensive Income (Loss) (Schedule of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 5,860
Ending balance	5,893
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	3	$ 27
Other comprehensive loss before reclassifications	0	0
Net other comprehensive loss attributable to Westlake Chemical Corporation	0	0
Ending balance	3	27
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(77)	(89)
Other comprehensive loss before reclassifications	(32)	(2)
Net other comprehensive loss attributable to Westlake Chemical Corporation	(32)	(2)
Ending balance	(109)	(91)
Accumulated Other Comprehensive Income (Loss) [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(74)	(62)
Other comprehensive loss before reclassifications	(32)	(2)
Net other comprehensive loss attributable to Westlake Chemical Corporation	(32)	(2)
Ending balance	$ (106)	$ (64)