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Supplemental Information (Restructuring Accrual Activity) (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
Restructuring Reserve [Roll Forward]
Charges	$ 3		$ 115	$ 21	$ 122
Pernis Facility Closure
Restructuring Reserve [Roll Forward]
Balances at beginning of period	198	$ 226		226
Charges	(4)	4				$ 247
Payments	(17)	(28)
Foreign currency translation	(2)	(4)
Balances at end of period	175	198		175		226
Cumulative charges recognized	307			307
Pernis Facility Closure \| Asset Write-offs
Restructuring Reserve [Roll Forward]
Charges						15
Pernis Facility Closure \| Asset Retirement Obligations
Restructuring Reserve [Roll Forward]
Balances at beginning of period	88	99		99
Charges	(3)	4
Payments	(11)	(13)
Foreign currency translation	(1)	(2)
Balances at end of period	73	88		73		99
Cumulative charges recognized	123			123
Pernis Facility Closure \| Severance and Separation Costs
Restructuring Reserve [Roll Forward]
Balances at beginning of period	16	25		25
Charges	1	2
Payments	(2)	(11)
Foreign currency translation	(1)	0
Balances at end of period	14	16		14		25
Cumulative charges recognized	30			30
Pernis Facility Closure \| Contract Termination and Other Costs
Restructuring Reserve [Roll Forward]
Balances at beginning of period	94	102		102
Charges	(2)	(2)
Payments	(4)	(4)
Foreign currency translation	0	(2)
Balances at end of period	88	94		88		102
Cumulative charges recognized	154			154
Chlorovinyls and Styrene Facility Closure
Restructuring Reserve [Roll Forward]
Balances at beginning of period	43	76		76
Charges	7	11				393
Payments	(24)	(44)
Balances at end of period	26	43		26		76
Cumulative charges recognized	94			94
Chlorovinyls and Styrene Facility Closure \| Asset Write-offs
Restructuring Reserve [Roll Forward]
Charges						30
Chlorovinyls and Styrene Facility Closure \| Asset Retirement Obligations
Restructuring Reserve [Roll Forward]
Balances at beginning of period	34	52		52
Charges	2	0
Payments	(16)	(18)
Balances at end of period	20	34		20		52
Cumulative charges recognized	54			54
Chlorovinyls and Styrene Facility Closure \| Severance and Separation Costs
Restructuring Reserve [Roll Forward]
Balances at beginning of period	4	17		17
Charges	1	3
Payments	(1)	(16)
Balances at end of period	4	4		4		17
Cumulative charges recognized	21			21
Chlorovinyls and Styrene Facility Closure \| Other Plant Shutdown Costs
Restructuring Reserve [Roll Forward]
Balances at beginning of period	5	7		7
Charges	4	8
Payments	(7)	(10)
Balances at end of period	2	$ 5		2		$ 7
Cumulative charges recognized	$ 19			$ 19