Guarantor Disclosures (Condensed Consolidating Financial Information Statement Of Operations) (Details) - USD ($) $ 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
Condensed Financial Statements, Captions [Line Items]
Net sales	$ 2,010	$ 2,109	$ 1,979	$ 1,943	$ 1,735	$ 1,280	$ 1,086	$ 975	$ 8,041	$ 5,076	$ 4,463
Cost of sales									6,272	4,095	3,278
Gross profit	498	498	405	368	282	203	241	255	1,769	981	1,185
Selling, general and administrative expenses									399	258	218
Amortization of intangibles									108	38	7
Transaction and integration-related costs									29	104	0
Income from operations	365	366	266	236	153	46	180	202	1,233	581	960
Interest expense									(159)	(79)	(35)
Other income (expense), net									7	56	38
Income before income taxes									1,081	558	963
Provision for (benefit from) income taxes									(258)	138	298
Equity in net income of subsidiaries									0	0	0
Net income	816	219	159	145	105	70	116	129	1,339	420	665
Net income attributable to noncontrolling interests									35	21	19
Net income attributable to Westlake Chemical Corporation	$ 802	$ 211	$ 153	$ 138	$ 99	$ 66	$ 111	$ 123	1,304	399	646
Comprehensive income attributable to Westlake Chemical Corporation									1,432	407	596
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net sales									(1,752)	(1,379)	(1,381)
Cost of sales									(1,725)	(1,357)	(1,361)
Gross profit									(27)	(22)	(20)
Selling, general and administrative expenses									(27)	(22)	(20)
Amortization of intangibles									0	0	0
Transaction and integration-related costs									0	0
Income from operations									0	0	0
Interest expense									179	82	42
Other income (expense), net									(179)	(82)	(42)
Income before income taxes									0	0	0
Provision for (benefit from) income taxes									0	0	0
Equity in net income of subsidiaries									(1,318)	(400)	(664)
Net income									(1,318)	(400)	(664)
Net income attributable to noncontrolling interests									0	0	0
Net income attributable to Westlake Chemical Corporation									(1,318)	(400)	(664)
Comprehensive income attributable to Westlake Chemical Corporation									(1,326)	(407)	(596)
Westlake Chemical Corporation [Member]
Condensed Financial Statements, Captions [Line Items]
Net sales									0	0	0
Cost of sales									0	0	0
Gross profit									0	0	0
Selling, general and administrative expenses									3	2	3
Amortization of intangibles									1	1	0
Transaction and integration-related costs									0	0
Income from operations									(4)	(3)	(3)
Interest expense									(154)	(83)	(42)
Other income (expense), net									154	77	20
Income before income taxes									(4)	(9)	(25)
Provision for (benefit from) income taxes									10	(8)	(7)
Equity in net income of subsidiaries									1,318	400	664
Net income									1,304	399	646
Net income attributable to noncontrolling interests									0	0	0
Net income attributable to Westlake Chemical Corporation									1,304	399	646
Comprehensive income attributable to Westlake Chemical Corporation									1,432	407	596
100% Owned Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net sales									6,650	4,010	3,558
Cost of sales									5,559	3,533	2,842
Gross profit									1,091	477	716
Selling, general and administrative expenses									292	178	146
Amortization of intangibles									81	27	5
Transaction and integration-related costs									27	103
Income from operations									691	169	565
Interest expense									(178)	(76)	(35)
Other income (expense), net									(3)	(14)	5
Income before income taxes									510	79	535
Provision for (benefit from) income taxes									(312)	115	275
Equity in net income of subsidiaries									0	0	0
Net income									822	(36)	260
Net income attributable to noncontrolling interests									0	0	0
Net income attributable to Westlake Chemical Corporation									822	(36)	260
Comprehensive income attributable to Westlake Chemical Corporation									833	11	261
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net sales									3,143	2,445	2,286
Cost of sales									2,438	1,919	1,797
Gross profit									705	526	489
Selling, general and administrative expenses									131	100	89
Amortization of intangibles									26	10	2
Transaction and integration-related costs									2	1
Income from operations									546	415	398
Interest expense									(6)	(2)	0
Other income (expense), net									35	75	55
Income before income taxes									575	488	453
Provision for (benefit from) income taxes									44	31	30
Equity in net income of subsidiaries									0	0	0
Net income									531	457	423
Net income attributable to noncontrolling interests									35	21	19
Net income attributable to Westlake Chemical Corporation									496	436	404
Comprehensive income attributable to Westlake Chemical Corporation									$ 493	$ 396	$ 335