Guarantor Disclosures (Condensed Consolidating Financial Information Balance Sheet) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	$ 1,531	$ 459	$ 663	$ 881
Accounts receivable, net	1,001	939
Inventories	900	801
Prepaid expenses and other current assets	30	48
Restricted cash	1	161
Total current assets	3,463	2,408
Property, plant and equipment, net	6,412	6,420
Goodwill	1,012	947	62
Customer relationships, net	616	611
Other intangible assets, net	161	176
Other assets, net	412	328
Total assets	12,076	10,890
Accounts payable	600	496
Accrued liabilities	657	538
Current portion of long-term debt, net	710	0
Term loan	0	149
Total current liabilities	1,967	1,183
Long-term debt, net	3,127	3,679
Deferred income taxes	1,111	1,650
Pension and other liabilities	502	486
Total liabilities	6,707	6,998
Total Westlake Chemical Corporation stockholders' equity	4,874	3,524
Noncontrolling interests	495	368
Total equity	5,369	3,892	3,562	3,202
Total liabilities and equity	12,076	10,890
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	0	0	0	0
Accounts receivable, net	(7,038)	(4,833)
Inventories	0	0
Prepaid expenses and other current assets	(79)	(37)
Restricted cash	0	0
Total current assets	(7,117)	(4,870)
Property, plant and equipment, net	0	0
Goodwill	0	0
Customer relationships, net	0	0
Other intangible assets, net	0	(25)
Other assets, net	(12,363)	(10,832)
Total assets	(19,480)	(15,727)
Accounts payable	(6,855)	(4,808)
Accrued liabilities	(262)	(61)
Current portion of long-term debt, net	0
Term loan		0
Total current liabilities	(7,117)	(4,869)
Long-term debt, net	(4,369)	(3,997)
Deferred income taxes	(7)	(23)
Pension and other liabilities	0	0
Total liabilities	(11,493)	(8,889)
Total Westlake Chemical Corporation stockholders' equity	(7,987)	(6,838)
Noncontrolling interests	0	0
Total equity	(7,987)	(6,838)
Total liabilities and equity	(19,480)	(15,727)
Westlake Chemical Corporation [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	1,089	147	303	656
Accounts receivable, net	3,331	2,118
Inventories	0	0
Prepaid expenses and other current assets	52	31
Restricted cash	0	0
Total current assets	4,472	2,296
Property, plant and equipment, net	0	0
Goodwill	0	0
Customer relationships, net	0	0
Other intangible assets, net	0	0
Other assets, net	10,706	9,170
Total assets	15,178	11,466
Accounts payable	6,367	4,331
Accrued liabilities	189	26
Current portion of long-term debt, net	710
Term loan		0
Total current liabilities	7,266	4,357
Long-term debt, net	3,034	3,585
Deferred income taxes	0	0
Pension and other liabilities	4	0
Total liabilities	10,304	7,942
Total Westlake Chemical Corporation stockholders' equity	4,874	3,524
Noncontrolling interests	0	0
Total equity	4,874	3,524
Total liabilities and equity	15,178	11,466
100% Owned Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	57	53	7	3
Accounts receivable, net	4,128	3,330
Inventories	654	598
Prepaid expenses and other current assets	26	42
Restricted cash	1	0
Total current assets	4,866	4,023
Property, plant and equipment, net	4,374	4,476
Goodwill	855	792
Customer relationships, net	479	468
Other intangible assets, net	88	131
Other assets, net	798	874
Total assets	11,460	10,764
Accounts payable	864	748
Accrued liabilities	484	390
Current portion of long-term debt, net	0
Term loan		0
Total current liabilities	1,348	1,138
Long-term debt, net	4,242	4,091
Deferred income taxes	1,026	1,581
Pension and other liabilities	347	361
Total liabilities	6,963	7,171
Total Westlake Chemical Corporation stockholders' equity	4,497	3,593
Noncontrolling interests	0	0
Total equity	4,497	3,593
Total liabilities and equity	11,460	10,764
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	385	259	$ 353	$ 222
Accounts receivable, net	580	324
Inventories	246	203
Prepaid expenses and other current assets	31	12
Restricted cash	0	161
Total current assets	1,242	959
Property, plant and equipment, net	2,038	1,944
Goodwill	157	155
Customer relationships, net	137	143
Other intangible assets, net	73	70
Other assets, net	1,271	1,116
Total assets	4,918	4,387
Accounts payable	224	225
Accrued liabilities	246	183
Current portion of long-term debt, net	0
Term loan		149
Total current liabilities	470	557
Long-term debt, net	220	0
Deferred income taxes	92	92
Pension and other liabilities	151	125
Total liabilities	933	774
Total Westlake Chemical Corporation stockholders' equity	3,490	3,245
Noncontrolling interests	495	368
Total equity	3,985	3,613
Total liabilities and equity	$ 4,918	$ 4,387