Accumulated Other Comprehensive Income (Loss) (Schedule of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balances	$ 11,043	$ 10,764
Ending balances	10,921	10,853
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balances	(144)	(98)
Net other comprehensive income attributable to Westlake Corporation	14	(34)
Ending balances	(130)	(132)
Pension and Other Post-Retirement Benefits Liability, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balances	54	4
Net other comprehensive income attributable to Westlake Corporation	0	1
Ending balances	54	5
Cumulative Foreign Currency Exchange, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balances	(198)	(102)
Net other comprehensive income attributable to Westlake Corporation	14	(35)
Ending balances	$ (184)	$ (137)