Consolidated Statements Of Changes In Stockholders' Equity Statement - USD ($) $ in Millions	Total	Common Stock	Common Stock, Held in Treasury	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interests [Member]
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
Beginning balances at Dec. 31, 2020	6,578	$ 1	$ (401)	569	5,938	(64)	535
Beginning balance, shares issued at Dec. 31, 2020		134,651,380
Beginning balance, Treasury shares at Dec. 31, 2020			6,821,174
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Westlake Chemical Corporation					242
Net income attributable to noncontrolling interests							11
Net income	253
Other comprehensive income	(7)					(6)	(1)
Shares issued—stock- based compensation (in shares)			(301,112)
Shares issued—stock-based compensation	9		$ 22	(13)
Stock-based compensation	8			8
Dividends declared	(35)				(35)
Distributions to noncontrolling interests	(11)						(11)
Noncontrolling Interest, Increase from Consolidating Previously Unconsolidated Subsidiary	30						30
Ending balances at Mar. 31, 2021	6,825	$ 1	$ (379)	564	6,145	(70)	564
Ending balance, shares issued at Mar. 31, 2021		134,651,380
Ending balance, Treasury shares at Mar. 31, 2021			6,520,062
Beginning balances at Dec. 31, 2020	6,578	$ 1	$ (401)	569	5,938	(64)	535
Beginning balance, shares issued at Dec. 31, 2020		134,651,380
Beginning balance, Treasury shares at Dec. 31, 2020			6,821,174
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Westlake Chemical Corporation	1,371
Net income attributable to noncontrolling interests	38
Net income	1,409
Other comprehensive income	(11)
Ending balances at Sep. 30, 2021	7,869	$ 1	$ (406)	576	7,202	(75)	571
Ending balance, shares issued at Sep. 30, 2021		134,651,380
Ending balance, Treasury shares at Sep. 30, 2021			6,830,317
Beginning balances at Mar. 31, 2021	6,825	$ 1	$ (379)	564	6,145	(70)	564
Beginning balance, shares issued at Mar. 31, 2021		134,651,380
Beginning balance, Treasury shares at Mar. 31, 2021			6,520,062
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Westlake Chemical Corporation					522
Net income attributable to noncontrolling interests							14
Net income	536
Other comprehensive income	15					14	1
Shares issued—stock- based compensation (in shares)			(18,397)
Shares issued—stock-based compensation	1		$ 1	0	0
Stock-based compensation	7			7
Dividends declared	(34)				(34)
Distributions to noncontrolling interests	(11)						(11)
Ending balances at Jun. 30, 2021	7,339		$ (378)	571	6,633	(56)	568
Ending balance, Treasury shares at Jun. 30, 2021			6,501,665
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Westlake Chemical Corporation	607				607
Net income attributable to noncontrolling interests	13						13
Net income	620
Other comprehensive income	(19)					(19)	0
Common stock repurchased, shares			355,800
Common stock repurchased	(30)		$ (30)
Shares issued—stock- based compensation (in shares)			(27,148)
Shares issued—stock-based compensation	0		$ 2	(2)	0
Stock-based compensation	7			7
Dividends declared	(38)				(38)
Distributions to noncontrolling interests	(10)						(10)
Ending balances at Sep. 30, 2021	$ 7,869	$ 1	$ (406)	$ 576	$ 7,202	$ (75)	$ 571
Ending balance, shares issued at Sep. 30, 2021		134,651,380
Ending balance, Treasury shares at Sep. 30, 2021			6,830,317