Consolidated Statements of Operations (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Net sales	$ 2,255	$ 2,109	$ 6,640	$ 6,031
Cost of sales	1,716	1,613	5,007	4,766
Gross profit	539	496	1,633	1,265
Selling, general and administrative expenses	114	98	337	298
Amortization of Intangibles	24	27	75	82
Transaction and integration-related costs	5	7	20	23
Income (loss) from operations	396	364	1,201	862
Other income (expense)
Interest expense	(28)	(40)	(96)	(119)
Other income, net	23	4	53	13
Income before income taxes	391	328	1,158	756
Provision for income taxes	73	109	255	233
Net income	318	219	903	523
Net income attributable to noncontrolling interests	10	8	30	21
Net income attributable to Westlake Chemical Corporation	$ 308	$ 211	$ 873	$ 502
Earnings per common share attributable to Westlake Chemical Corporation:
Basic (usd per share)	$ 2.36	$ 1.62	$ 6.70	$ 3.87
Diluted (usd per share)	$ 2.35	$ 1.61	$ 6.67	$ 3.85
Weighted average common shares outstanding:
Basic (in shares)	129,427,328	129,069,186	129,512,097	129,033,597
Diluted (in shares)	130,052,292	129,888,968	130,183,201	129,789,965