Segment Information (Segment Reporting Information) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Net sales	$ 2,235	$ 1,979	$ 4,385	$ 3,922
Income (loss) from operations	404	264	805	498
Depreciation and amortization	156	145	312	295
Other income (expense), net	8	2	30	9
Provision for (benefit from) income taxes	93	68	182	124
Additions to property, plant and equipment	158	147	312	281
Operating Segments [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net sales	482	489	985	1,032
Income (loss) from operations	158	143	321	323
Depreciation and amortization	33	35	67	76
Other income (expense), net	1	1	3	2
Provision for (benefit from) income taxes	36	36	73	94
Additions to property, plant and equipment	26	24	48	49
Operating Segments [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net sales	1,753	1,490	3,400	2,890
Income (loss) from operations	271	141	537	211
Depreciation and amortization	120	107	238	214
Other income (expense), net	4	0	16	6
Provision for (benefit from) income taxes	69	39	130	54
Additions to property, plant and equipment	128	114	258	222
Operating Segments [Member] | Polyethylene [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net sales	387	358	756	744
Operating Segments [Member] | Styrene, Feedstock And Other [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net sales	95	131	229	288
Operating Segments [Member] | PVC, Caustic Soda And Other [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net sales	1,396	1,157	2,754	2,288
Operating Segments [Member] | Building Products [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net sales	357	333	646	602
Corporate and other [Member]
Segment Reporting Information [Line Items]
Income (loss) from operations	(25)	(20)	(53)	(36)
Depreciation and amortization	3	3	7	5
Other income (expense), net	3	1	11	1
Provision for (benefit from) income taxes	(12)	(7)	(21)	(24)
Additions to property, plant and equipment	4	9	6	10
Intersegment sales [Member]
Segment Reporting Information [Line Items]
Net sales	113	98	233	184
Intersegment sales [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net sales	112	98	232	184
Intersegment sales [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net sales	$ 1	$ 0	$ 1	$ 0