Earnings (Loss) and Dividends per Share (Schedule of Net Income Attributable to Common Stockholders) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Earnings and Dividends Per Share [Abstract]
Net income (loss) attributable to Westlake Corporation	$ 6	$ (782)	$ 97	$ (964)
Net income (loss) attributable to participating securities	0	(4)	1	(5)
Net income (loss) attributable to common stockholders	$ 6	$ (778)	$ 96	$ (959)

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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+ Details