Consolidated Statements of Operations (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Net sales	$ 2,859	$ 1,709	$ 5,216	$ 3,641
Cost of sales	1,987	1,540	3,835	3,189
Gross profit	872	169	1,381	452
Selling, general and administrative expenses	125	104	261	224
Amortization of intangibles	27	27	54	54
Restructuring, transaction and integration-related costs	0	2	0	2
Income from operations	720	36	1,066	172
Other income (expense)
Interest expense	(36)	(40)	(69)	(71)
Other income, net	10	9	22	20
Income before income taxes	694	5	1,019	121
Provision for (benefit from) income taxes	158	(19)	230	(60)
Net income	536	24	789	181
Net income attributable to noncontrolling interests	14	9	25	21
Net income attributable to Westlake Chemical Corporation	$ 522	$ 15	$ 764	$ 160
Earnings per common share attributable to Westlake Chemical Corporation:
Basic (in dollars per share)	$ 4.06	$ 0.11	$ 5.94	$ 1.24
Diluted (in dollars per share)	$ 4.04	$ 0.11	$ 5.91	$ 1.24
Weighted average common shares outstanding:
Basic (in shares)	128,142,997	127,680,478	128,049,852	127,958,921
Diluted (in shares)	128,877,860	127,823,629	128,681,776	128,133,300