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Supplemental Information (Additional Information) (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2026	Mar. 31, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Dec. 31, 2025
Related Party Transaction [Line Items]
Other assets, net	$ 761			$ 761		$ 784
Deferred turnaround costs, net	397			397		433
Accrued Liabilities and Other Liabilities [Abstract]
Accrued and other liabilities	1,429			1,429		1,490
Accrued rebates	239			239		225
Operating lease liabilities, current	128			128		138
Restructuring Charges [Abstract]
Restructuring, transaction and integration-related costs	3		$ 115	21	$ 122
Pernis Facility Closure
Restructuring Charges [Abstract]
Restructuring, transaction and integration-related costs	(4)	$ 4				247
Pernis Facility Closure \| Asset Write-offs
Restructuring Charges [Abstract]
Restructuring, transaction and integration-related costs						15
Pernis Facility Closure \| Severance and Separation Costs
Restructuring Charges [Abstract]
Restructuring, transaction and integration-related costs	1	2
Expected restructuring charges remaining	4			4
Pernis Facility Closure \| Contract Termination and Other Costs
Restructuring Charges [Abstract]
Restructuring, transaction and integration-related costs	(2)	(2)
Chlorovinyls and Styrene Facility Closure
Restructuring Charges [Abstract]
Restructuring, transaction and integration-related costs	7	11				393
Chlorovinyls and Styrene Facility Closure \| Asset Write-offs
Restructuring Charges [Abstract]
Restructuring, transaction and integration-related costs						30
Chlorovinyls and Styrene Facility Closure \| Severance and Separation Costs
Restructuring Charges [Abstract]
Restructuring, transaction and integration-related costs	1	$ 3
Expected restructuring charges remaining	1			1
Chlorovinyls and Styrene Facility Closure \| Accelerated Depreciation and Amortization
Restructuring Charges [Abstract]
Restructuring, transaction and integration-related costs						287
Chlorovinyls and Styrene Facility Closure \| Contract Termination and Other Costs
Restructuring Charges [Abstract]
Expected restructuring charges remaining	6			6
Related Party
Accrued Liabilities and Other Liabilities [Abstract]
Other liabilities, current	$ 22			$ 22		$ 31
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-07-01
Related Party Transaction [Line Items]
Remaining performance obligation term	20 years			20 years
Remaining performance obligations	$ 185			$ 185