Accumulated Other Comprehensive Income (Loss) (Schedule of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 6,043
Ending balance	7,298
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(24)	$ 3
Net other comprehensive income (loss) attributable to Westlake Chemical Corporation	0	0
Ending balance	(24)	3
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(40)	(77)
Net other comprehensive income (loss) attributable to Westlake Chemical Corporation	(11)	5
Ending balance	(51)	(72)
Accumulated Other Comprehensive Income (Loss) [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(64)	(74)
Net other comprehensive income (loss) attributable to Westlake Chemical Corporation	(11)	5
Ending balance	$ (75)	$ (69)