Consolidated Statements Of Changes In Stockholders' Equity Statement - 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]
Beginning balances at Dec. 31, 2016	$ 3,892	$ 1	$ (319)	$ 551	$ 3,412	$ (121)	$ 368
Beginning balance, shares issued at Dec. 31, 2016		134,651,380
Beginning balance, Treasury shares at Dec. 31, 2016			5,726,377
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	523				502		21
Other comprehensive loss	110					108	2
Shares issued—stock- based compensation (in shares)			(174,684)
Shares issued—stock- based compensation	2		$ 4	(2)
Stock-based compensation	10			10
Dividends declared	(76)				(76)
Distributions to noncontrolling interests	(21)						(21)
Issuance of Westlake Chemical Partners LP common units	111						111
Ending balances at Sep. 30, 2017	4,551	$ 1	$ (315)	559	3,838	(13)	481
Ending balance, shares issued at Sep. 30, 2017		134,651,380
Ending balance, Treasury shares at Sep. 30, 2017			5,551,693
Beginning balances at Dec. 31, 2017	5,369	$ 1	$ (302)	555	4,613	7	495
Beginning balance, shares issued at Dec. 31, 2017		134,651,380
Beginning balance, Treasury shares at Dec. 31, 2017			5,232,875
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	903				873		30
Other comprehensive loss	(33)					(31)	(2)
Common stock repurchased shares			515,853
Common Stock repurchased	(49)		$ (49)
Shares issued—stock- based compensation (in shares)			(262,564)
Shares issued—stock- based compensation	8		$ 14	(6)
Stock-based compensation	13			13
Dividends declared	(87)				(87)
Distributions to noncontrolling interests	(37)						(37)
Ending balances at Sep. 30, 2018	6,088	$ 1	$ (337)	$ 562	5,400	$ (24)	$ 486
Ending balance, shares issued at Sep. 30, 2018		134,651,380
Ending balance, Treasury shares at Sep. 30, 2018			5,486,164
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting change	$ 1				$ 1