v3.26.1
Accumulated Other Comprehensive Loss (Schedule of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($)
$ in Millions
 3 Months Ended
Jun. 30, 2026
Mar. 31, 2026
Jun. 30, 2025
Mar. 31, 2025
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Beginning balances $ 9,051 $ 9,295 $ 10,921 $ 11,043
Ending balances 9,208 9,051 10,791 10,921
Accumulated Other Comprehensive Loss        
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Beginning balances (99) (80) (130) (144)
Net other comprehensive income (loss) attributable to Westlake Corporation (17) (19) 66 14
Ending balances (116) (99) (64) (130)
Pension and Other Post-Retirement Benefits Liability, Net of Tax        
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Beginning balances 44 44 54 54
Net other comprehensive income (loss) attributable to Westlake Corporation 0 0 1 0
Ending balances 44 44 55 54
Cumulative Foreign Currency Exchange, Net of Tax        
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Beginning balances (143) (125) (184) (198)
Net other comprehensive income (loss) attributable to Westlake Corporation (17) (18) 65 14
Ending balances (160) (143) (119) (184)
Available-for-sale Securities, Net of Tax        
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Beginning balances 0 1 0 0
Net other comprehensive income (loss) attributable to Westlake Corporation 0 (1) 0 0
Ending balances $ 0 $ 0 $ 0 $ 0