Segment and Geographic Information (Segment Reporting Information) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net sales	$ 1,995	$ 2,255	$ 2,235	$ 2,150	$ 2,010	$ 2,109	$ 1,979	$ 1,943	$ 8,635	$ 8,041	$ 5,076
Income from operations	$ 207	$ 396	$ 404	$ 401	$ 363	$ 364	$ 264	$ 234	1,408	1,225	583
Depreciation and amortization									641	601	378
Other income, net									52	15	54
Provision for (benefit from) income taxes									300	(258)	138
Payments to Acquire Property, Plant, and Equipment									702	577	629
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales									8,635	8,041	5,076
Operating Segments [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net sales									2,019	2,051	1,894
Income from operations									573	655	558
Depreciation and amortization									138	145	136
Other income, net									4	3	5
Provision for (benefit from) income taxes									128	63	175
Payments to Acquire Property, Plant, and Equipment									110	97	324
Operating Segments [Member] | Olefins [Member] | Polyethylene [Member]
Segment Reporting Information [Line Items]
Net sales									1,519	1,518	1,463
Operating Segments [Member] | Olefins [Member] | Styrene, Feedstock And Other [Member]
Segment Reporting Information [Line Items]
Net sales									500	533	431
Operating Segments [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net sales									6,616	5,990	3,182
Income from operations									913	639	176
Depreciation and amortization									491	449	238
Other income, net									35	7	1
Provision for (benefit from) income taxes									212	(302)	25
Payments to Acquire Property, Plant, and Equipment									585	459	302
Operating Segments [Member] | Vinyls [Member] | PVC, Caustic Soda And Other [Member]
Segment Reporting Information [Line Items]
Net sales									5,359	4,769	2,493
Operating Segments [Member] | Vinyls [Member] | Building Products [Member]
Segment Reporting Information [Line Items]
Net sales									1,257	1,221	689
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Income from operations									(78)	(69)	(151)
Depreciation and amortization									12	7	4
Other income, net									13	5	48
Provision for (benefit from) income taxes									(40)	(19)	(62)
Payments to Acquire Property, Plant, and Equipment									7	21	3
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Net sales									502	394	191
Intersegment Eliminations [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net sales									500	393	165
Intersegment Eliminations [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net sales									$ 2	$ 1	$ 26