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]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares		134,663,244
Treasury Stock, Shares			4,444,898
Beginning Balances 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	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 (in shares)			(112,611)
Stock-based compensation	7		$ 3	4
Dividends declared	(97)				(97)
Distributions to noncontrolling interests	(17)						(17)
Issuance of Westlake Chemical Partners LP common units	68						68
Ending Balances at Dec. 31, 2016	3,892	$ 1	$ (319)	551	3,412	(121)	368
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares		134,651,380
Treasury Stock, Shares			5,726,377
Net income	1,339				1,304		35
Other comprehensive income	133					128	5
Common stock repurchased, shares			0
Shares issued—stock- based compensation, shares		0	(493,502)
Shares issued—stock-based compensation	11	$ 0	$ 17	6
Stock-based compensation (in shares)			0
Stock-based compensation	14		$ 0	14
Dividends declared	(103)				(103)
Distributions to noncontrolling interests	(28)						(28)
Issuance of Westlake Chemical Partners LP common units	111			(4)			115
Ending Balances at Dec. 31, 2017	$ 5,369	$ 1	$ (302)	555	4,613	7	495
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares	134,651,380	134,651,380
Treasury Stock, Shares	5,232,875		5,232,875
Reclassification of certain tax effects to retained earnings					(13)	13
Net income	$ 1,034				996		38
Other comprehensive income	(84)					(82)	(2)
Common stock repurchased, shares			1,368,881
Common stock repurchased	(106)		$ (106)				0
Shares issued—stock- based compensation, shares		0	(418,631)
Shares issued—stock-based compensation	$ 9	$ 0	$ 26	17
Stock-based compensation (in shares)	(323,182)		0
Stock-based compensation	$ 18		$ 0	18
Dividends declared	(120)				(120)
Distributions to noncontrolling interests	(45)						(45)
Ending Balances at Dec. 31, 2018	$ 6,076	$ 1	$ (382)	$ 556	5,477	$ (62)	$ 486
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares	134,651,380	134,651,380
Treasury Stock, Shares	6,183,125		6,183,125
Cumulative effect of accounting change	$ 1				$ 1