Guarantor Disclosures (Condensed Consolidating Financial Information Statement Of Cash Flows) (Details) - USD ($) $ in Millions			3 Months Ended								12 Months Ended
	Sep. 29, 2017	Aug. 04, 2014	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 income (loss)			$ 816	$ 219	$ 159	$ 145	$ 105	$ 70	$ 116	$ 129	$ 1,339	$ 420	$ 665
Depreciation and amortization											601	378	246
Deferred income taxes											(534)	101	40
Net changes in working capital and other											132	(65)	128
Net cash provided by operating activities											1,538	834	1,079
Acquisition of business, net of cash acquired											(13)	(2,438)	16
Additions to property, plant and equipment											(577)	(629)	(491)
Additions to cost method investment											(66)	(17)	0
Proceeds from disposition of equity method investment											0	0	28
Proceeds from sales and maturities of securities											0	663	49
Purchase of securities											0	(138)	(605)
Other											4	(4)	(3)
Net cash used for investing activities											(652)	(2,563)	(1,006)
Intercompany financing											0	0	0
Receivable under the investment management agreement											0
Debt issuance costs											(6)	(36)	0
Dividends paid											(103)	(97)	(92)
Distributions to noncontrolling interests											(28)	(17)	(15)
Proceeds from debt issuance and drawdown of revolver											233	608	53
Net proceeds from issuance of Westlake Partners common units	$ 111	$ 286									111	0	0
Proceeds from senior notes issuance											745	1,429	0
Repayment of term loan											(150)	0	0
Restricted cash associated with term loan											154	(154)	0
Repayment of notes payable											(257)	(13)	(74)
Repurchase of common stock for treasury											0	(67)	(163)
Repayment of revolver											(550)	(125)	0
Other											11	5	4
Net cash provided by (used for) financing activities											160	1,533	(287)
Effect of exchange rate changes on cash and cash equivalents											26	(8)	(4)
Net increase (decrease) in cash and cash equivalents											1,072	(204)	(218)
Cash and cash equivalents at beginning of the year						459				663	459	663	881
Cash and cash equivalents at end of the year			1,531				459				1,531	459	663
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)											(1,318)	(400)	(664)
Depreciation and amortization											0	0	0
Deferred income taxes											0	0	0
Net changes in working capital and other											1,318	400	664
Net cash provided by operating activities											0	0	0
Acquisition of business, net of cash acquired											0	0	0
Additions to property, plant and equipment											0	0	0
Additions to cost method investment											0	0
Proceeds from disposition of equity method investment													0
Proceeds from sales and maturities of securities												0	0
Purchase of securities												0	0
Other											136	0	0
Net cash used for investing activities											136	0	0
Intercompany financing											0	0	0
Receivable under the investment management agreement											(136)
Debt issuance costs											0	0
Dividends paid											0	0	0
Distributions to noncontrolling interests											0	0	0
Proceeds from debt issuance and drawdown of revolver											0	0	0
Net proceeds from issuance of Westlake Partners common units											0
Proceeds from senior notes issuance											0	0
Repayment of term loan											0
Restricted cash associated with term loan											0	0
Repayment of notes payable											0	0	0
Repurchase of common stock for treasury												0	0
Repayment of revolver											0	0
Other											0	0	0
Net cash provided by (used for) financing activities											(136)	0	0
Effect of exchange rate changes on cash and cash equivalents											0	0	0
Net increase (decrease) in cash and cash equivalents											0	0	0
Cash and cash equivalents at beginning of the year						0				0	0	0	0
Cash and cash equivalents at end of the year			0				0				0	0	0
Westlake Chemical Corporation [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)											1,304	399	646
Depreciation and amortization											0	0	0
Deferred income taxes											12	1	0
Net changes in working capital and other											(1,327)	(437)	(659)
Net cash provided by operating activities											(11)	(37)	(13)
Acquisition of business, net of cash acquired											0	0	0
Additions to property, plant and equipment											0	0	0
Additions to cost method investment											0	0
Proceeds from disposition of equity method investment													0
Proceeds from sales and maturities of securities												658	49
Purchase of securities												(138)	(556)
Other											0	0	0
Net cash used for investing activities											0	520	(507)
Intercompany financing											746	(2,199)	418
Receivable under the investment management agreement											136
Debt issuance costs											(6)	(35)
Dividends paid											(103)	(97)	(92)
Distributions to noncontrolling interests											0	0	0
Proceeds from debt issuance and drawdown of revolver											225	450	0
Net proceeds from issuance of Westlake Partners common units											0
Proceeds from senior notes issuance											745	1,429
Repayment of term loan											0
Restricted cash associated with term loan											0	0
Repayment of notes payable											(251)	0	0
Repurchase of common stock for treasury												(67)	(163)
Repayment of revolver											(550)	(125)
Other											11	5	4
Net cash provided by (used for) financing activities											953	(639)	167
Effect of exchange rate changes on cash and cash equivalents											0	0	0
Net increase (decrease) in cash and cash equivalents											942	(156)	(353)
Cash and cash equivalents at beginning of the year						147				303	147	303	656
Cash and cash equivalents at end of the year			1,089				147				1,089	147	303
100% Owned Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)											822	(36)	260
Depreciation and amortization											395	217	114
Deferred income taxes											(535)	103	39
Net changes in working capital and other											41	90	93
Net cash provided by operating activities											723	374	506
Acquisition of business, net of cash acquired											(13)	(2,502)	0
Additions to property, plant and equipment											(407)	(275)	(215)
Additions to cost method investment											(66)	(17)
Proceeds from disposition of equity method investment													28
Proceeds from sales and maturities of securities												0	0
Purchase of securities												0	(49)
Other											2	(4)	(3)
Net cash used for investing activities											(484)	(2,798)	(239)
Intercompany financing											(611)	2,207	(590)
Receivable under the investment management agreement											0
Debt issuance costs											0	0
Dividends paid											0	0	0
Distributions to noncontrolling interests											376	263	327
Proceeds from debt issuance and drawdown of revolver											0	0	0
Net proceeds from issuance of Westlake Partners common units											0
Proceeds from senior notes issuance											0	0
Repayment of term loan											0
Restricted cash associated with term loan											0	0
Repayment of notes payable											0	0	0
Repurchase of common stock for treasury												0	0
Repayment of revolver											0	0
Other											0	0	0
Net cash provided by (used for) financing activities											(235)	2,470	(263)
Effect of exchange rate changes on cash and cash equivalents											0	0	0
Net increase (decrease) in cash and cash equivalents											4	46	4
Cash and cash equivalents at beginning of the year						53				7	53	7	3
Cash and cash equivalents at end of the year			57				53				57	53	7
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)											531	457	423
Depreciation and amortization											206	161	132
Deferred income taxes											(11)	(3)	1
Net changes in working capital and other											100	(118)	30
Net cash provided by operating activities											826	497	586
Acquisition of business, net of cash acquired											0	64	16
Additions to property, plant and equipment											(170)	(354)	(276)
Additions to cost method investment											0	0
Proceeds from disposition of equity method investment													0
Proceeds from sales and maturities of securities												5	0
Purchase of securities												0	0
Other											(134)	0	0
Net cash used for investing activities											(304)	(285)	(260)
Intercompany financing											(135)	(8)	172
Receivable under the investment management agreement											0
Debt issuance costs											0	(1)
Dividends paid											0	0	0
Distributions to noncontrolling interests											(404)	(280)	(342)
Proceeds from debt issuance and drawdown of revolver											8	158	53
Net proceeds from issuance of Westlake Partners common units											111
Proceeds from senior notes issuance											0	0
Repayment of term loan											(150)
Restricted cash associated with term loan											154	(154)
Repayment of notes payable											(6)	(13)	(74)
Repurchase of common stock for treasury												0	0
Repayment of revolver											0	0
Other											0	0	0
Net cash provided by (used for) financing activities											(422)	(298)	(191)
Effect of exchange rate changes on cash and cash equivalents											26	(8)	(4)
Net increase (decrease) in cash and cash equivalents											126	(94)	131
Cash and cash equivalents at beginning of the year						$ 259				$ 353	259	353	222
Cash and cash equivalents at end of the year			$ 385				$ 259				$ 385	$ 259	$ 353