Fair Value Measurements (Summary of Carrying and Fair Values of Long Term Debt) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 07, 2016	Sep. 06, 2016	Dec. 31, 2015
Senior Notes [Member] | 4.625% Senior Notes Due 2021 (New Westlake 2021 Notes) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Maturity date	2021
Stated interest rate (percent)	4.625%
Senior Notes [Member] | 4.625% Senior Notes Due 2021 (Existing Axiall 2021 Notes) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Maturity date	2021
Stated interest rate (percent)	4.625%		4.625%
Senior Notes [Member] | 3.60% Senior Notes Due 2022 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Maturity date	2022
Stated interest rate (percent)	3.60%
Senior Notes [Member] | 4.875% Senior Notes Due 2023 (New Westlake 2023 Notes) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Maturity date	2023
Stated interest rate (percent)	4.875%	4.875%
Senior Notes [Member] | 4.875% Senior Notes Due 2023 (Existing Axiall 2023 Notes) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Maturity date	2023
Stated interest rate (percent)	4.875%
Senior Notes [Member] | 3.6% Senior Notes Due 2026 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Maturity date	2026
Stated interest rate (percent)	3.60%
Senior Notes [Member] | Loan related to tax-exempt waste disposal revenue bonds due 2027 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Maturity date	2027
Senior Notes [Member] | 6 1/2% Senior Notes Due 2029 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Maturity date	2029
Stated interest rate (percent)	6.50%
Senior Notes [Member] | 6 3/4% Senior Notes Due 2032 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Maturity date	2032
Stated interest rate (percent)	6.75%
Senior Notes [Member] | 2035 GO Zone 6 1/2% Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Maturity date	2035
Stated interest rate (percent)	6.50%
Senior Notes [Member] | 2035 IKE Zone 6 1/2% Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Maturity date	2035
Stated interest rate (percent)	6.50%
Senior Notes [Member] | 5% Senior Notes Due 2046 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Maturity date	2046
Stated interest rate (percent)	5.00%
Carrying Value [Member] | Loan related to tax-exempt waste disposal revenue bonds due 2027 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	$ 10,889			$ 10,889
Carrying Value [Member] | Line of Credit [Member] | Unsecured Revolving Credit Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Revolving credit facility	325,000			0
Carrying Value [Member] | Senior Notes [Member] | 4.625% Senior Notes Due 2021 (New Westlake 2021 Notes) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	653,256			0
Carrying Value [Member] | Senior Notes [Member] | 4.625% Senior Notes Due 2021 (Existing Axiall 2021 Notes) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	66,243			0
Carrying Value [Member] | Senior Notes [Member] | 3.60% Senior Notes Due 2022 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	248,024			247,768
Carrying Value [Member] | Senior Notes [Member] | 4.875% Senior Notes Due 2023 (New Westlake 2023 Notes) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	447,751			0
Carrying Value [Member] | Senior Notes [Member] | 4.875% Senior Notes Due 2023 (Existing Axiall 2023 Notes) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	16,769			0
Carrying Value [Member] | Senior Notes [Member] | 3.6% Senior Notes Due 2026 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	739,082			0
Carrying Value [Member] | Senior Notes [Member] | 6 1/2% Senior Notes Due 2029 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	99,066			99,011
Carrying Value [Member] | Senior Notes [Member] | 6 3/4% Senior Notes Due 2032 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	248,087			247,998
Carrying Value [Member] | Senior Notes [Member] | 2035 GO Zone 6 1/2% Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	88,149			88,116
Carrying Value [Member] | Senior Notes [Member] | 2035 IKE Zone 6 1/2% Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	64,390			64,366
Carrying Value [Member] | Senior Notes [Member] | 5% Senior Notes Due 2046 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	673,879			0
Fair Value [Member] | Loan related to tax-exempt waste disposal revenue bonds due 2027 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	10,889			10,889
Fair Value [Member] | Line of Credit [Member] | Unsecured Revolving Credit Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Revolving credit facility	325,000			0
Fair Value [Member] | Senior Notes [Member] | 4.625% Senior Notes Due 2021 (New Westlake 2021 Notes) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	653,715			0
Fair Value [Member] | Senior Notes [Member] | 4.625% Senior Notes Due 2021 (Existing Axiall 2021 Notes) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	66,058			0
Fair Value [Member] | Senior Notes [Member] | 3.60% Senior Notes Due 2022 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	251,480			244,828
Fair Value [Member] | Senior Notes [Member] | 4.875% Senior Notes Due 2023 (New Westlake 2023 Notes) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	454,151			0
Fair Value [Member] | Senior Notes [Member] | 4.875% Senior Notes Due 2023 (Existing Axiall 2023 Notes) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	16,954			0
Fair Value [Member] | Senior Notes [Member] | 3.6% Senior Notes Due 2026 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	752,055			0
Fair Value [Member] | Senior Notes [Member] | 6 1/2% Senior Notes Due 2029 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	117,726			117,153
Fair Value [Member] | Senior Notes [Member] | 6 3/4% Senior Notes Due 2032 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	265,383			268,490
Fair Value [Member] | Senior Notes [Member] | 2035 GO Zone 6 1/2% Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	105,298			106,491
Fair Value [Member] | Senior Notes [Member] | 2035 IKE Zone 6 1/2% Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	76,837			76,741
Fair Value [Member] | Senior Notes [Member] | 5% Senior Notes Due 2046 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	$ 705,985			$ 0