Supplemental Information (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Supplemental Information (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Related Party Transaction [Line Items]
Contract with Customer, Liability, Payment Advance	$ 70
Contract with Customer, Liability	147	$ 147	$ 62	$ 52	$ 42
Contract with Customer, Liability, Revenue Recognized		(5)	(5)	(5)
Contract with Customer, Liability, Increases due to Cash Received and Due, Excluding Amounts Recognized as Revenue		90	15	15
Accrued Liabilities
Accrued and other liabilities	1,490	1,490	1,362
Accrued rebates	225	225	232
Accrued and other liabilities	$ 138	138	128
Non-Cash Investing Activity [Abstract]
Capital Expenditures Incurred but Not yet Paid		128	157	184
Restructuring and Related Activities [Abstract]
Restructuring, transaction and integration-related costs		640	91	28
Other Income and Expenses [Abstract]
Interest income		100	153	104
Pension Gain, Other		32	19	28
Income from unconsolidated subsidiaries		16	18	19
Supplemental Cash Flow Information [Abstract]
Operating Lease, Payments		177	154	139
Right-of-use assets obtained in exchange for operating lease obligations		141	246	240
Interest paid, net of interest capitalized		157	153	159
Income taxes paid		$ 104	422	$ 421
Pension Plan \| United States
Other Income and Expenses [Abstract]
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Settlement Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Other income, net
Pension Plan \| Foreign Plan
Other Income and Expenses [Abstract]
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Settlement Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Other income, net
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Related Party Transaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	20 years	20 years
Revenue, Remaining Performance Obligation, Amount	$ 187	$ 187
Pernis Facility Closure
Restructuring and Related Activities [Abstract]
Restructuring, transaction and integration-related costs		232	75
Restructuring Charges		247	75
Inventory Write-down		15
Chlorovinyls and Styrene Facility Closure
Restructuring and Related Activities [Abstract]
Restructuring, transaction and integration-related costs		386
Restructuring Charges		$ 393
Restructuring Charges, Statement of Income or Comprehensive Income [Extensible Enumeration]		Restructuring, transaction and integration-related costs
Inventory Write-down		$ 7
Huasu PVC unit
Restructuring and Related Activities [Abstract]
Restructuring, transaction and integration-related costs		9
Employee Severance \| Pernis Facility Closure
Restructuring and Related Activities [Abstract]
Restructuring Charges		23	4
Restructuring and Related Cost, Expected Cost Remaining	7	7
Inventory Write-down		0
Employee Severance \| Chlorovinyls and Styrene Facility Closure
Restructuring and Related Activities [Abstract]
Restructuring Charges		17
Restructuring and Related Cost, Expected Cost Remaining	4	4
Inventory Write-down		0
Asset Retirement Obligations \| Pernis Facility Closure
Restructuring and Related Activities [Abstract]
Restructuring Charges		98	24
Inventory Write-down		0
Asset Retirement Obligations \| Chlorovinyls and Styrene Facility Closure
Restructuring and Related Activities [Abstract]
Restructuring Charges		52
Inventory Write-down		0
Inventory Write-Down \| Pernis Facility Closure
Restructuring and Related Activities [Abstract]
Restructuring Charges		15	0
Inventory Write-down		15
Inventory Write-Down \| Chlorovinyls and Styrene Facility Closure
Restructuring and Related Activities [Abstract]
Restructuring Charges		30
Inventory Write-down		7
Contract Termination Costs \| Pernis Facility Closure
Restructuring and Related Activities [Abstract]
Restructuring Charges		111	47
Inventory Write-down		0
Facility Closing \| Pernis Facility Closure
Restructuring and Related Activities [Abstract]
Restructuring and Related Cost, Expected Cost Remaining	3	3
Facility Closing \| Chlorovinyls and Styrene Facility Closure
Restructuring and Related Activities [Abstract]
Restructuring Charges		7
Restructuring and Related Cost, Expected Cost Remaining	21	21
Inventory Write-down		0
Accelerated Depreciation and Amortization \| Chlorovinyls and Styrene Facility Closure
Restructuring and Related Activities [Abstract]
Restructuring Charges		287
Inventory Write-down		0
Restructuring Charges \| Chlorovinyls and Styrene Facility Closure
Restructuring and Related Activities [Abstract]
Restructuring Charges		317
Related Party
Accrued Liabilities
Other Liabilities, Current	$ 31	$ 31	$ 26

WESTLAKE CORP 10-K