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Accumulated Other Comprehensive Income (Loss) (Schedule of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Increase (Decrease) in Stockholders' Equity [Roll Forward]    
Beginning balance $ 6,043  
Ending balance 6,261  
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]    
Increase (Decrease) in Stockholders' Equity [Roll Forward]    
Beginning balance (24) $ 3
Net other Comprehensive Loss, attributable to Westlake Chemical Corporation 0 0
Ending balance (24) 3
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]    
Increase (Decrease) in Stockholders' Equity [Roll Forward]    
Beginning balance (40) (77)
Net other Comprehensive Loss, attributable to Westlake Chemical Corporation (6) (32)
Ending balance (46) (109)
Accumulated Other Comprehensive Income (Loss) [Member]    
Increase (Decrease) in Stockholders' Equity [Roll Forward]    
Beginning balance (64) (74)
Net other Comprehensive Loss, attributable to Westlake Chemical Corporation (6) (32)
Ending balance $ (70) $ (106)