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, 2018	$ 6,076	$ 1	$ (382)	$ 556	$ 5,477	$ (62)	$ 486
Beginning balance, shares issued at Dec. 31, 2018		134,651,380
Beginning balance, Treasury shares at Dec. 31, 2018			6,183,125
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Westlake Chemical Corporation					72
Net income attributable to noncontrolling interests							10
Net income	82
Other comprehensive income	(2)					(2)	0
Shares issued—stock- based compensation (in shares)			(124,052)
Shares issued—stock-based compensation	0		$ 11	(8)	(3)
Stock-based compensation	7			7
Dividends declared	(33)				(33)
Distributions to noncontrolling interests	(8)						(8)
Issuance of Westlake Chemical Partners LP common units	63			(2)			65
Ending balances at Mar. 31, 2019	6,185	$ 1	$ (371)	553	5,513	(64)	553
Ending balance, shares issued at Mar. 31, 2019		134,651,380
Ending balance, Treasury shares at Mar. 31, 2019			6,059,073
Beginning balances at Dec. 31, 2018	6,076	$ 1	$ (382)	556	5,477	(62)	486
Beginning balance, shares issued at Dec. 31, 2018		134,651,380
Beginning balance, Treasury shares at Dec. 31, 2018			6,183,125
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Westlake Chemical Corporation	349
Net income attributable to noncontrolling interests	28
Net income	377
Other comprehensive income	(5)
Ending balances at Sep. 30, 2019	6,362	$ 1	$ (396)	561	5,724	(66)	538
Ending balance, shares issued at Sep. 30, 2019		134,651,380
Ending balance, Treasury shares at Sep. 30, 2019			6,515,203
Beginning balances at Mar. 31, 2019	6,185	$ 1	$ (371)	553	5,513	(64)	553
Beginning balance, shares issued at Mar. 31, 2019		134,651,380
Beginning balance, Treasury shares at Mar. 31, 2019			6,059,073
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Westlake Chemical Corporation					119
Net income attributable to noncontrolling interests							10
Net income	129
Other comprehensive income	13					14	(1)
Common stock repurchased, shares			342,740
Common stock repurchased	(20)		$ (20)
Shares issued—stock- based compensation (in shares)			(19,173)
Shares issued—stock-based compensation	0		$ 1	(1)	0
Stock-based compensation	6			6
Dividends declared	(32)				(32)
Distributions to noncontrolling interests	(22)						(22)
Ending balances at Jun. 30, 2019	6,259	$ 1	$ (390)	558	5,600	(50)	540
Ending balance, shares issued at Jun. 30, 2019		134,651,380
Ending balance, Treasury shares at Jun. 30, 2019			6,382,640
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Westlake Chemical Corporation	158				158
Net income attributable to noncontrolling interests	8						8
Net income	166
Other comprehensive income	(16)					(16)	0
Common stock repurchased, shares			174,972
Common stock repurchased	(10)		$ (10)
Shares issued—stock- based compensation (in shares)			(42,409)
Shares issued—stock-based compensation	0		$ 4	(3)	(1)
Stock-based compensation	6			6
Dividends declared	(33)				(33)
Distributions to noncontrolling interests	(10)						(10)
Ending balances at Sep. 30, 2019	6,362	$ 1	$ (396)	561	5,724	(66)	538
Ending balance, shares issued at Sep. 30, 2019		134,651,380
Ending balance, Treasury shares at Sep. 30, 2019			6,515,203
Beginning balances at Dec. 31, 2019	6,403	$ 1	$ (377)	553	5,757	(74)	543
Beginning balance, shares issued at Dec. 31, 2019		134,651,380
Beginning balance, Treasury shares at Dec. 31, 2019			6,266,609
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Westlake Chemical Corporation					145
Net income attributable to noncontrolling interests							12
Net income	157
Other comprehensive income	(32)					(32)	0
Common stock repurchased, shares			995,529
Common stock repurchased	(54)		$ (54)
Shares issued—stock- based compensation (in shares)			(282,476)
Shares issued—stock-based compensation	2		$ 18	(8)	(8)
Stock-based compensation	6			6
Dividends declared	(34)				(34)
Distributions to noncontrolling interests	(10)						(10)
Ending balances at Mar. 31, 2020	6,438	$ 1	$ (413)	551	5,860	(106)	545
Ending balance, shares issued at Mar. 31, 2020		134,651,380
Ending balance, Treasury shares at Mar. 31, 2020			6,979,662
Beginning balances at Dec. 31, 2019	6,403	$ 1	$ (377)	553	5,757	(74)	543
Beginning balance, shares issued at Dec. 31, 2019		134,651,380
Beginning balance, Treasury shares at Dec. 31, 2019			6,266,609
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Westlake Chemical Corporation	217
Net income attributable to noncontrolling interests	33
Net income	250
Other comprehensive income	7
Ending balances at Sep. 30, 2020	6,488	$ 1	$ (409)	563	5,863	(69)	539
Ending balance, shares issued at Sep. 30, 2020		134,651,380
Ending balance, Treasury shares at Sep. 30, 2020			6,930,624
Beginning balances at Mar. 31, 2020	6,438	$ 1	$ (413)	551	5,860	(106)	545
Beginning balance, shares issued at Mar. 31, 2020		134,651,380
Beginning balance, Treasury shares at Mar. 31, 2020			6,979,662
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Westlake Chemical Corporation					15
Net income attributable to noncontrolling interests							9
Net income	24
Other comprehensive income	20					19	1
Shares issued—stock- based compensation (in shares)			(16,331)
Shares issued—stock-based compensation	0		$ 2	(1)	(1)
Stock-based compensation	8			8
Dividends declared	(34)				(34)
Distributions to noncontrolling interests	(19)						(19)
Ending balances at Jun. 30, 2020	6,437	$ 1	$ (411)	558	5,840	(87)	536
Ending balance, shares issued at Jun. 30, 2020		134,651,380
Ending balance, Treasury shares at Jun. 30, 2020			6,963,331
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Westlake Chemical Corporation	57				57
Net income attributable to noncontrolling interests	12						12
Net income	69
Other comprehensive income	19					18	1
Shares issued—stock- based compensation (in shares)			(32,707)
Shares issued—stock-based compensation	0		$ 2	(2)	0
Stock-based compensation	7			7
Dividends declared	(34)				(34)
Distributions to noncontrolling interests	(10)						(10)
Ending balances at Sep. 30, 2020	$ 6,488	$ 1	$ (409)	$ 563	$ 5,863	$ (69)	$ 539
Ending balance, shares issued at Sep. 30, 2020		134,651,380
Ending balance, Treasury shares at Sep. 30, 2020			6,930,624