Segment Information (Segment Reporting Information) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Revenues	$ 2,255	$ 2,109	$ 6,640	$ 6,031
Income (loss) from operations	396	364	1,201	862
Depreciation and amortization	161	154	473	449
Other income (expense), net	23	4	53	13
Provision for (benefit from) income taxes	73	109	255	233
Additions to property, plant and equipment	195	133	507	414
Operating Segments [Member] \| Olefins [Member]
Segment Reporting Information [Line Items]
Revenues	541	502	1,526	1,534
Income (loss) from operations	162	166	483	489
Depreciation and amortization	35	35	102	111
Other income (expense), net	1	0	4	2
Provision for (benefit from) income taxes	34	58	107	152
Additions to property, plant and equipment	33	21	81	70
Operating Segments [Member] \| Vinyls [Member]
Segment Reporting Information [Line Items]
Revenues	1,714	1,607	5,114	4,497
Income (loss) from operations	251	214	788	425
Depreciation and amortization	124	118	362	332
Other income (expense), net	16	1	32	7
Provision for (benefit from) income taxes	44	61	174	115
Additions to property, plant and equipment	162	108	420	330
Operating Segments [Member] \| Polyethylene [Member] \| Olefins [Member]
Segment Reporting Information [Line Items]
Revenues	396	377	1,152	1,121
Operating Segments [Member] \| Styrene, Feedstock And Other [Member] \| Olefins [Member]
Segment Reporting Information [Line Items]
Revenues	145	125	374	413
Operating Segments [Member] \| PVC, Caustic Soda And Other [Member] \| Vinyls [Member]
Segment Reporting Information [Line Items]
Revenues	1,372	1,253	4,126	3,541
Operating Segments [Member] \| Building Products [Member] \| Vinyls [Member]
Segment Reporting Information [Line Items]
Revenues	342	354	988	956
Corporate and other [Member]
Segment Reporting Information [Line Items]
Income (loss) from operations	(17)	(16)	(70)	(52)
Depreciation and amortization	2	1	9	6
Other income (expense), net	6	3	17	4
Provision for (benefit from) income taxes	(5)	(10)	(26)	(34)
Additions to property, plant and equipment	0	4	6	14
Intersegment sales [Member]
Segment Reporting Information [Line Items]
Revenues	136	108	369	292
Intersegment sales [Member] \| Olefins [Member]
Segment Reporting Information [Line Items]
Revenues	136	107	368	291
Intersegment sales [Member] \| Vinyls [Member]
Segment Reporting Information [Line Items]
Revenues	$ 0	$ 1	$ 1	$ 1

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