Guarantor Disclosures (Condensed Consolidating Financial Information Statement of Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 505	$ 428	$ 505	$ 428	$ 1,554	$ 646
Net income	288	159	585	304
Depreciation and amortization	156	145	312	295
Deferred income taxes			45	15
Net changes in working capital and other			(393)	(134)
Net cash provided by operating activities			549	480
Additions to property, plant and equipment	(158)	(147)	(312)	(281)
Additions to investments in unconsolidated subsidiaries			(45)	(31)
Other			3	2
Net cash used for investing activities			(354)	(310)
Intercompany financing			0	0
Dividends paid			(54)	(49)
Distributions to noncontrolling interests			(29)	(16)
Proceeds from notes payable and drawdown of revolver			6	178
Repayment of term loan			0	(150)
Repayment of revolver			0	(360)
Redemption and repayment of notes payable			(1,173)	(5)
Other			8	1
Net cash used for financing activities			(1,242)	(401)
Effect of exchange rate changes on cash, cash equivalents and restricted cash			(2)	13
Net decrease in cash, cash equivalents and restricted cash			(1,049)	(218)
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0	0	0	0	0
Net income	(270)	(158)	(552)	(293)
Depreciation and amortization			0	0
Deferred income taxes			0	0
Net changes in working capital and other			552	293
Net cash provided by operating activities			0	0
Additions to property, plant and equipment			0	0
Additions to investments in unconsolidated subsidiaries			0	0
Other			0	0
Net cash used for investing activities			0	0
Intercompany financing			0	0
Dividends paid			0	0
Distributions to noncontrolling interests			0	0
Proceeds from notes payable and drawdown of revolver			0	0
Repayment of term loan				0
Repayment of revolver				0
Redemption and repayment of notes payable			0	0
Other			0	0
Net cash used for financing activities			0	0
Effect of exchange rate changes on cash, cash equivalents and restricted cash			0	0
Net decrease in cash, cash equivalents and restricted cash			0	0
Westlake Chemical Corporation [Member]
Condensed Financial Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	258	47	258	47	1,089	147
Net income	278	153	565	291
Depreciation and amortization			0	0
Deferred income taxes			1	0
Net changes in working capital and other			(533)	(400)
Net cash provided by operating activities			33	(109)
Additions to property, plant and equipment			0	0
Additions to investments in unconsolidated subsidiaries			0	0
Other			0	0
Net cash used for investing activities			0	0
Intercompany financing			347	242
Dividends paid			(54)	(49)
Distributions to noncontrolling interests			0	0
Proceeds from notes payable and drawdown of revolver			0	175
Repayment of term loan				0
Repayment of revolver				(360)
Redemption and repayment of notes payable			(1,165)	0
Other			8	1
Net cash used for financing activities			(864)	9
Effect of exchange rate changes on cash, cash equivalents and restricted cash			0	0
Net decrease in cash, cash equivalents and restricted cash			(831)	(100)
100% Owned Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	62	40	62	40	79	78
Net income	133	51	268	73
Depreciation and amortization			208	194
Deferred income taxes			40	15
Net changes in working capital and other			(459)	(26)
Net cash provided by operating activities			57	256
Additions to property, plant and equipment			(248)	(199)
Additions to investments in unconsolidated subsidiaries			(35)	(31)
Other			3	2
Net cash used for investing activities			(280)	(228)
Intercompany financing			(1)	(254)
Dividends paid			0	0
Distributions to noncontrolling interests			207	189
Proceeds from notes payable and drawdown of revolver			0	0
Repayment of term loan				0
Repayment of revolver				0
Redemption and repayment of notes payable			0	(1)
Other			0	0
Net cash used for financing activities			206	(66)
Effect of exchange rate changes on cash, cash equivalents and restricted cash			0	0
Net decrease in cash, cash equivalents and restricted cash			(17)	(38)
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	185	341	185	341	$ 386	$ 421
Net income	$ 147	$ 113	304	233
Depreciation and amortization			104	101
Deferred income taxes			4	0
Net changes in working capital and other			47	(1)
Net cash provided by operating activities			459	333
Additions to property, plant and equipment			(64)	(82)
Additions to investments in unconsolidated subsidiaries			(10)	0
Other			0	0
Net cash used for investing activities			(74)	(82)
Intercompany financing			(346)	12
Dividends paid			0	0
Distributions to noncontrolling interests			(236)	(205)
Proceeds from notes payable and drawdown of revolver			6	3
Repayment of term loan				(150)
Repayment of revolver				0
Redemption and repayment of notes payable			(8)	(4)
Other			0	0
Net cash used for financing activities			(584)	(344)
Effect of exchange rate changes on cash, cash equivalents and restricted cash			(2)	13
Net decrease in cash, cash equivalents and restricted cash			$ (201)	$ (80)