Quarterly Financial Information (Summary Of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 2,010	$ 2,109	$ 1,979	$ 1,943	$ 1,735	$ 1,280	$ 1,086	$ 975	$ 8,041	$ 5,076	$ 4,463
Gross profit	498	498	405	368	282	203	241	255	1,769	981	1,185
Income from operations	365	366	266	236	153	46	180	202	1,233	581	960
Net income	816	219	159	145	105	70	116	129	1,339	420	665
Net income attributable to Westlake Chemical Corporation	$ 802	$ 211	$ 153	$ 138	$ 99	$ 66	$ 111	$ 123	$ 1,304	$ 399	$ 646
Basic (in dollars per share)	$ 6.18	$ 1.62	$ 1.18	$ 1.07	$ 0.76	$ 0.51	$ 0.85	$ 0.94	$ 10.05	$ 3.07	$ 4.88
Diluted (in dollars per share)	$ 6.15	$ 1.61	$ 1.17	$ 1.06	$ 0.76	$ 0.51	$ 0.85	$ 0.94	$ 10.00	$ 3.06	$ 4.86