Consolidated Statements Of Changes In Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock [Member]	Common Stock, Held In Treasury [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interests [Member]
Number of shares, beginning balance at Dec. 31, 2014		134,679,064	1,787,546
Total equity, beginning balance at Dec. 31, 2014	$ 3,202	$ 1	$ (96)	$ 530	$ 2,556	$ (79)	$ 290
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	665				646		19
Other comprehensive income (loss)	(50)					(50)	0
Common stock repurchased, shares			2,701,937
Common stock repurchased	(163)		$ (163)				0
Shares issued—stock- based compensation, shares		(15,820)	(44,585)
Shares issued—stock- based compensation	1	$ 0	$ 1	0
Stock-based compensation, net of tax on stock options exercised	12			12
Dividends declared	(92)				(92)
Distributions to noncontrolling interests	(15)						(15)
Issuance of Westlake Chemical Partners LP common units	2						2
Number of shares, ending balance at Dec. 31, 2015		134,663,244	4,444,898
Total equity, ending balance at Dec. 31, 2015	3,562	$ 1	$ (258)	542	3,110	(129)	296
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	420				399		21
Other comprehensive income (loss)	8					8	0
Common stock repurchased, shares			1,511,109
Common stock repurchased	(67)		$ (67)				0
Shares issued—stock- based compensation, shares		(11,864)	(117,019)
Shares issued—stock- based compensation	8	$ 0	$ 3	5
Stock-based compensation, net of tax on stock options exercised (in shares)			(112,611)
Stock-based compensation, net of tax on stock options exercised	7		$ 3	4
Dividends declared	(97)				(97)
Distributions to noncontrolling interests	(17)						(17)
Issuance of Westlake Chemical Partners LP common units	68						68
Number of shares, ending balance at Dec. 31, 2016		134,651,380	5,726,377
Total equity, ending balance at Dec. 31, 2016	3,892	$ 1	$ (319)	551	3,412	(121)	368
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,339				1,304		35
Other comprehensive income (loss)	133					128	5
Shares issued—stock- based compensation, shares		0	(493,502)
Shares issued—stock- based compensation	$ 11	$ 0	$ 17	(6)
Stock-based compensation, net of tax on stock options exercised (in shares)	(401,505)		0
Stock-based compensation, net of tax on stock options exercised	$ 14		$ 0	14
Dividends declared	(103)				(103)
Distributions to noncontrolling interests	(28)						(28)
Issuance of Westlake Chemical Partners LP common units	111			(4)			115
Number of shares, ending balance at Dec. 31, 2017		134,651,380	5,232,875
Total equity, ending balance at Dec. 31, 2017	$ 5,369	$ 1	$ (302)	$ 555	$ 4,613	$ 7	$ 495