Segment Information (Sales) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Net sales	$ 2,108,889	$ 1,279,028	$ 6,030,666	$ 3,340,276
Income (loss) from operations	365,747	46,563	868,161	428,777
Depreciation and amortization	153,634	94,229	448,533	227,193
Other income (expense), net	2,058	41,265	6,591	52,091
Provision for (benefit from) income taxes	108,619	(6,552)	232,690	129,332
Capital expenditures	133,369	180,170	414,271	467,330
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	2,108,889	1,279,028	6,030,666	3,340,276
Operating Segments [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net sales	502,243	497,365	1,534,472	1,422,869
Income (loss) from operations	165,438	118,475	488,532	408,274
Depreciation and amortization	35,029	36,649	111,244	95,582
Other income (expense), net	(184)	1,101	1,555	3,706
Provision for (benefit from) income taxes	58,218	31,956	152,482	136,429
Capital expenditures	20,960	96,469	70,043	285,359
Operating Segments [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net sales	1,606,646	781,663	4,496,194	1,917,407
Income (loss) from operations	216,515	22,235	431,276	136,559
Depreciation and amortization	117,490	56,136	331,585	128,691
Other income (expense), net	(970)	(1,226)	1,087	1,722
Provision for (benefit from) income taxes	60,784	(3,912)	114,979	29,655
Capital expenditures	107,515	83,523	329,968	180,392
Operating Segments [Member] | Polyethylene [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net sales	377,269	380,810	1,121,603	1,098,500
Operating Segments [Member] | Styrene, Feedstock And Other [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net sales	124,974	116,555	412,869	324,369
Operating Segments [Member] | PVC, Caustic Soda And Other [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net sales	1,252,963	599,276	3,541,409	1,492,650
Operating Segments [Member] | Building Products [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net sales	353,683	182,387	954,785	424,757
Corporate and other [Member]
Segment Reporting Information [Line Items]
Income (loss) from operations	(16,206)	(94,147)	(51,647)	(116,056)
Depreciation and amortization	1,115	1,444	5,704	2,920
Other income (expense), net	3,212	41,390	3,949	46,663
Provision for (benefit from) income taxes	(10,383)	(34,596)	(34,771)	(36,752)
Capital expenditures	4,894	178	14,260	1,579
Intersegment sales [Member]
Segment Reporting Information [Line Items]
Net sales	106,982	32,744	291,529	88,575
Intersegment sales [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net sales	106,722	30,614	290,658	85,856
Intersegment sales [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net sales	$ 260	$ 2,130	$ 871	$ 2,719