Guarantor Disclosures (Condensed Consolidating Financial Information Balance Sheets) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	$ 482	$ 1,531
Accounts receivable, net	1,261	1,001
Inventories	905	900
Prepaid expenses and other current assets	46	31
Total current assets	2,694	3,463
Property, plant and equipment, net	6,468	6,412
Goodwill	1,006	1,012
Customer relationships, net	569	616
Other intangible assets, net	149	161
Other assets, net	460	412
Total assets	11,346	12,076
Accounts payable	582	600
Accrued liabilities	604	657
Current portion of long-term debt, net	0	710
Total current liabilities	1,186	1,967
Long-term debt, net	2,666	3,127
Deferred income taxes	1,153	1,111
Pension and other liabilities	495	502
Total liabilities	5,500	6,707
Total Westlake Chemical Corporation stockholders' equity	5,362	4,874
Noncontrolling interests	484	495
Total equity	5,846	5,369	$ 4,209	$ 3,892
Total liabilities and equity	11,346	12,076
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	0	0
Accounts receivable, net	(9,856)	(7,038)
Inventories	0	0
Prepaid expenses and other current assets	(174)	(79)
Total current assets	(10,030)	(7,117)
Property, plant and equipment, net	0	0
Goodwill	0	0
Customer relationships, net	0	0
Other intangible assets, net	0	0
Other assets, net	(12,840)	(12,363)
Total assets	(22,870)	(19,480)
Accounts payable	(9,680)	(6,855)
Accrued liabilities	(348)	(262)
Current portion of long-term debt, net		0
Total current liabilities	(10,028)	(7,117)
Long-term debt, net	(4,375)	(4,369)
Deferred income taxes	(13)	(7)
Pension and other liabilities	0	0
Total liabilities	(14,416)	(11,493)
Total Westlake Chemical Corporation stockholders' equity	(8,454)	(7,987)
Noncontrolling interests	0	0
Total equity	(8,454)	(7,987)
Total liabilities and equity	(22,870)	(19,480)
Westlake Chemical Corporation [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	258	1,089
Accounts receivable, net	4,963	3,331
Inventories	0	0
Prepaid expenses and other current assets	158	52
Total current assets	5,379	4,472
Property, plant and equipment, net	0	0
Goodwill	0	0
Customer relationships, net	0	0
Other intangible assets, net	0	0
Other assets, net	11,188	10,706
Total assets	16,567	15,178
Accounts payable	8,356	6,367
Accrued liabilities	183	189
Current portion of long-term debt, net		710
Total current liabilities	8,539	7,266
Long-term debt, net	2,656	3,034
Deferred income taxes	0	0
Pension and other liabilities	10	4
Total liabilities	11,205	10,304
Total Westlake Chemical Corporation stockholders' equity	5,362	4,874
Noncontrolling interests	0	0
Total equity	5,362	4,874
Total liabilities and equity	16,567	15,178
100% Owned Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	40	57
Accounts receivable, net	5,488	4,128
Inventories	651	654
Prepaid expenses and other current assets	39	27
Total current assets	6,218	4,866
Property, plant and equipment, net	4,466	4,374
Goodwill	855	855
Customer relationships, net	447	479
Other intangible assets, net	81	88
Other assets, net	800	798
Total assets	12,867	11,460
Accounts payable	1,675	864
Accrued liabilities	514	484
Current portion of long-term debt, net		0
Total current liabilities	2,189	1,348
Long-term debt, net	4,161	4,242
Deferred income taxes	1,072	1,026
Pension and other liabilities	336	347
Total liabilities	7,758	6,963
Total Westlake Chemical Corporation stockholders' equity	5,109	4,497
Noncontrolling interests	0	0
Total equity	5,109	4,497
Total liabilities and equity	12,867	11,460
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	184	385
Accounts receivable, net	666	580
Inventories	254	246
Prepaid expenses and other current assets	23	31
Total current assets	1,127	1,242
Property, plant and equipment, net	2,002	2,038
Goodwill	151	157
Customer relationships, net	122	137
Other intangible assets, net	68	73
Other assets, net	1,312	1,271
Total assets	4,782	4,918
Accounts payable	231	224
Accrued liabilities	255	246
Current portion of long-term debt, net		0
Total current liabilities	486	470
Long-term debt, net	224	220
Deferred income taxes	94	92
Pension and other liabilities	149	151
Total liabilities	953	933
Total Westlake Chemical Corporation stockholders' equity	3,345	3,490
Noncontrolling interests	484	495
Total equity	3,829	3,985
Total liabilities and equity	$ 4,782	$ 4,918