Long-Term Debt (Schedule of Long-term Debt) (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Principal Amount	$ 2,715	$ 3,853
Unamortized Premium (Discount) and Debt Issuance Costs	(48)	(16)
Net, Long-term Debt	2,667	3,837
Long-term Debt, Current Maturities	0	710
Long-term Debt, Gross Excluding Current Maturities	2,715	3,165
Debt Instrument, Unamortized Premium (Discount) and Debt Issuance Cost, Net, Excluding Current Maturities	(48)	(38)
Long-term Debt, Excluding Current Maturities	$ 2,667	3,127
Senior Notes [Member] \| 3.60% Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2022
Stated interest rate (percent)	3.60%
Principal Amount	$ 250	250
Unamortized Premium (Discount) and Debt Issuance Costs	(1)	(1)
Net, Long-term Debt	$ 249	249
Senior Notes [Member] \| 3.6% Senior Notes Due 2026 [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2026
Stated interest rate (percent)	3.60%
Principal Amount	$ 750	750
Unamortized Premium (Discount) and Debt Issuance Costs	(9)	(10)
Net, Long-term Debt	$ 741	740
Senior Notes [Member] \| Loan related to tax-exempt waste disposal revenue bonds due 2027 [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2027
Principal Amount	$ 11	11
Unamortized Premium (Discount) and Debt Issuance Costs	0	0
Net, Long-term Debt	$ 11	11
Senior Notes [Member] \| 6 1/2% Senior Notes Due 2029 [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2029
Stated interest rate (percent)	6.50%
Principal Amount	$ 100	100
Unamortized Premium (Discount) and Debt Issuance Costs	(1)	(1)
Net, Long-term Debt	$ 99	99
Senior Notes [Member] \| 2035 GO Zone 6 1/2% Notes [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2035
Stated interest rate (percent)	6.50%
Principal Amount	$ 89	89
Unamortized Premium (Discount) and Debt Issuance Costs	(1)	(1)
Net, Long-term Debt	$ 88	88
Senior Notes [Member] \| 2035 IKE Zone 6 1/2% Notes [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2035
Stated interest rate (percent)	6.50%
Principal Amount	$ 65	65
Unamortized Premium (Discount) and Debt Issuance Costs	0	0
Net, Long-term Debt	$ 65	65
Senior Notes [Member] \| 5% Senior Notes Due 2046 [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2046
Stated interest rate (percent)	5.00%
Principal Amount	$ 700	700
Unamortized Premium (Discount) and Debt Issuance Costs	(25)	(25)
Net, Long-term Debt	$ 675	675
Senior Notes [Member] \| 4.375% Senior Notes Due 2047 [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2047
Stated interest rate (percent)	4.375%
Principal Amount	$ 500	500
Unamortized Premium (Discount) and Debt Issuance Costs	(9)	(9)
Net, Long-term Debt	$ 491	491
Senior Notes [Member] \| 3.50% Senior Notes Due 2032 [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2032
Stated interest rate (percent)	3.50%
Principal Amount	$ 250	250
Unamortized Premium (Discount) and Debt Issuance Costs	(2)	(2)
Net, Long-term Debt	$ 248	248
Senior Notes [Member] \| 4.625% Senior Notes Due 2021 (New Westlake 2021 Notes) [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2021
Stated interest rate (percent)	4.625%
Principal Amount	$ 0	625
Unamortized Premium (Discount) and Debt Issuance Costs	0	20
Net, Long-term Debt	$ 0	645
Senior Notes [Member] \| 4.625% Senior Notes Due 2021 (Existing Axiall 2021 Notes) [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2021
Stated interest rate (percent)	4.625%
Principal Amount	$ 0	63
Unamortized Premium (Discount) and Debt Issuance Costs	0	2
Net, Long-term Debt	$ 0	65
Senior Notes [Member] \| 4.875% Senior Notes Due 2023 (New Westlake 2023 Notes) [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2023
Stated interest rate (percent)	4.875%
Principal Amount	$ 0	434
Unamortized Premium (Discount) and Debt Issuance Costs	0	11
Net, Long-term Debt	$ 0	445
Senior Notes [Member] \| 4.875% Senior Notes Due 2023 (Existing Axiall 2023 Notes) [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2023
Stated interest rate (percent)	4.875%
Principal Amount	$ 0	16
Unamortized Premium (Discount) and Debt Issuance Costs	0	0
Net, Long-term Debt	0	16
Senior Notes [Member] \| 4.625% Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Long-Term Debt, Gross, Current Maturities	0	688
Debt Instrument, Unamortized Premium (Discount) and debt issuance cost, net, Current Maturities	0	22
Long-term Debt, Current Maturities	$ 0	$ 710

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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