Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 318	$ 219	$ 903	$ 523
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Plan Amendments, Tax Effect [Abstract]
Pension and other post-retirement benefits reserves adjustment	12	1	12	2
Income tax provision on pension and other post-retirement benefits liability	(3)	(1)	(3)	(1)
Foreign Currency Translation Adjustment, by Component [Abstract]
Foreign currency translation	0	40	(43)	111
Income tax benefit (provision) on foreign currency translation	0	0	1	(2)
Other comprehensive income (loss)	9	40	(33)	110
Comprehensive income	327	259	870	633
Comprehensive income attributable to noncontrolling interests, net of tax of $1 for the three months ended September 30, 2018 and 2017; and net of tax of $3 and $2 for the nine months ended September 30, 2018 and 2017, respectively.	10	8	28	23
Comprehensive income attributable to Westlake Chemical Corporation	$ 317	$ 251	$ 842	$ 610