Quarterly Financial Information (Unaudited) (Summary Of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 1,883	$ 2,066	$ 2,144	$ 2,025	$ 1,995	$ 2,255	$ 2,235	$ 2,150	$ 8,118	$ 8,635	$ 8,041
Gross profit	250	371	340	299	354	539	552	542	1,260	1,987	1,761
Income from operations	102	226	194	134	207	396	404	401	656	1,408	1,225
Net income	85	166	129	82	131	318	288	297	462	1,034	1,339
Net income attributable to Westlake Chemical Corporation	$ 72	$ 158	$ 119	$ 72	$ 123	$ 308	$ 278	$ 287	$ 421	$ 996	$ 1,304
Basic (in dollars per share)	$ 0.56	$ 1.22	$ 0.92	$ 0.56	$ 0.95	$ 2.36	$ 2.13	$ 2.21	$ 3.26	$ 7.66	$ 10.05
Diluted (in dollars per share)	$ 0.56	$ 1.22	$ 0.92	$ 0.55	$ 0.95	$ 2.35	$ 2.12	$ 2.20	$ 3.25	$ 7.62	$ 10.00