Long-Term Debt (Exchange Offers) (Details) - USD ($) $ in Thousands	Mar. 27, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Aug. 10, 2016
Debt Instrument [Line Items]
Principal amount		$ 3,602,889	$ 3,677,889
Senior Notes [Member] | 3.60% Percentage Senior Notes Due 2026 [Member]
Debt Instrument [Line Items]
Principal amount					$ 750,000
Stated interest rate (percent)					3.60%
Exchange Offer Percentage	99.9667%
Senior Notes [Member] | 5.0% Percentage Senior Notes Due 2046 [Member]
Debt Instrument [Line Items]
Principal amount					$ 700,000
Stated interest rate (percent)					5.00%
Exchange Offer Percentage	100.00%
Senior Notes [Member] | 4.625% Senior Notes Due 2021 (New Westlake 2021 Notes) [Member]
Debt Instrument [Line Items]
Principal amount		$ 624,793	624,793
Stated interest rate (percent)		4.625%		4.625%
Senior Notes [Member] | 4.875% Senior Notes Due 2023 (New Westlake 2023 Notes) [Member]
Debt Instrument [Line Items]
Principal amount		$ 433,793	433,793
Stated interest rate (percent)		4.875%		4.875%
Senior Notes [Member] | 4.625% Senior Notes Due 2021 (Existing Axiall 2021 Notes) [Member]
Debt Instrument [Line Items]
Principal amount		$ 63,207	63,207	$ 688,000
Stated interest rate (percent)		4.625%		4.625%
Exchange Offer Percentage	99.9717%
Senior Notes [Member] | 4.875% Senior Notes Due 2023 (Existing Axiall 2023 Notes) [Member]
Debt Instrument [Line Items]
Principal amount		$ 16,207	$ 16,207	$ 450,000
Stated interest rate (percent)		4.875%		4.875%
Exchange Offer Percentage	100.00%