Segment And Geographic Information (Segment Reporting Information) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net sales	$ 2,010	$ 2,109	$ 1,979	$ 1,943	$ 1,735	$ 1,280	$ 1,086	$ 975	$ 8,041	$ 5,076	$ 4,463
Income from operations	$ 365	$ 366	$ 266	$ 236	$ 153	$ 46	$ 180	$ 202	1,233	581	960
Depreciation and amortization									601	378	246
Other income, net									7	56	38
Provision for (benefit from) income taxes									(258)	138	298
Payments to Acquire Property, Plant, and Equipment									577	629	491
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales									8,041	5,076	4,463
Operating Segments [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net sales									2,051	1,894	2,260
Income from operations									655	558	747
Depreciation and amortization									145	136	111
Other income, net									3	5	5
Provision for (benefit from) income taxes									63	175	243
Payments to Acquire Property, Plant, and Equipment									97	324	305
Operating Segments [Member] | Olefins [Member] | Polyethylene [Member]
Segment Reporting Information [Line Items]
Net sales									1,518	1,463	1,651
Operating Segments [Member] | Olefins [Member] | Styrene, Feedstock And Other [Member]
Segment Reporting Information [Line Items]
Net sales									533	431	609
Operating Segments [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net sales									5,990	3,182	2,203
Income from operations									647	174	255
Depreciation and amortization									449	238	134
Other income, net									(1)	3	8
Provision for (benefit from) income taxes									(302)	25	64
Payments to Acquire Property, Plant, and Equipment									459	302	176
Operating Segments [Member] | Vinyls [Member] | PVC, Caustic Soda And Other [Member]
Segment Reporting Information [Line Items]
Net sales									4,769	2,493	1,718
Operating Segments [Member] | Vinyls [Member] | Building Products [Member]
Segment Reporting Information [Line Items]
Net sales									1,221	689	485
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Income from operations									(69)	(151)	(42)
Depreciation and amortization									7	4	1
Other income, net									5	48	25
Provision for (benefit from) income taxes									(19)	(62)	(9)
Payments to Acquire Property, Plant, and Equipment									21	3	10
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Net sales									394	191	108
Intersegment Eliminations [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net sales									393	165	107
Intersegment Eliminations [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net sales									$ 1	$ 26	$ 1