Quarterly Financial Information (Unaudited) (Summary Of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 1,995	$ 2,255	$ 2,235	$ 2,150	$ 2,010	$ 2,109	$ 1,979	$ 1,943	$ 8,635	$ 8,041	$ 5,076
Gross profit	354	539	552	542	496	496	403	366	1,987	1,761	983
Income from operations	207	396	404	401	363	364	264	234	1,408	1,225	583
Net income	131	318	288	297	816	219	159	145	1,034	1,339	420
Net income attributable to Westlake Chemical Corporation	$ 123	$ 308	$ 278	$ 287	$ 802	$ 211	$ 153	$ 138	$ 996	$ 1,304	$ 399
Basic (in dollars per share)	$ 0.95	$ 2.36	$ 2.13	$ 2.21	$ 6.18	$ 1.62	$ 1.18	$ 1.07	$ 7.66	$ 10.05	$ 3.07
Diluted (in dollars per share)	$ 0.95	$ 2.35	$ 2.12	$ 2.20	$ 6.15	$ 1.61	$ 1.17	$ 1.06	$ 7.62	$ 10.00	$ 3.06