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Accumulated Other Comprehensive Income (Loss) (Schedule of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($)
$ in Millions
6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Increase (Decrease) in Stockholders' Equity [Roll Forward]    
Beginning balance $ 6,043  
Ending balance 6,771  
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]    
Increase (Decrease) in Stockholders' Equity [Roll Forward]    
Beginning balance (24) $ 3
Net other comprehensive income (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 income (loss) attributable to Westlake Chemical Corporation 8 (13)
Ending balance (32) (90)
Accumulated Other Comprehensive Income (Loss) [Member]    
Increase (Decrease) in Stockholders' Equity [Roll Forward]    
Beginning balance (64) (74)
Net other comprehensive income (loss) attributable to Westlake Chemical Corporation 8 (13)
Ending balance $ (56) $ (87)