Unaudited Interim Consolidated Statement Equity - USD ($) $ in Millions	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss), Net
Balance as of the beginning of the period (in shares) at Dec. 31, 2024			61,499,640
Balance as of the beginning of the period (in shares) at Dec. 31, 2024		109,327,556
Balance as of the beginning of the period at Dec. 31, 2024		$ 0	$ (5,486)	$ 409	$ 11,054	$ (848)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock option exercises, shares		0
Stock option exercises		$ 0
Stock awards (in shares)		176,799
Stock awards		$ 0
Issuance of treasury stock under stock plans (in shares)			(87,055)
Issuance of treasury stock under stock plans			$ 3
Stock-based compensation, net of tax				16
Net earnings (loss) attributable to Celanese Corporation	$ (1,184)				(1,184)
Common stock dividends					(9)
Other comprehensive income (loss), net of tax	1					(1)
Balance as of the end of the period (in shares) at Sep. 30, 2025		109,504,355
Balance as of the end of the period at Sep. 30, 2025	3,954	$ 0	$ (5,483)	425	9,861	(849)
Balance as of the end of the period (in shares) at Sep. 30, 2025			61,412,585
Balance as of the beginning of the period, noncontrolling interest at Dec. 31, 2024	434
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss) attributable to noncontrolling interests	11
Other comprehensive income (loss), net of tax	2
Distributions/dividends to noncontrolling interests	(22)
Balance as of the end of the period, noncontrolling interest at Sep. 30, 2025	425
Balance as of the beginning of the period (in shares) at Jun. 30, 2025			61,412,585
Balance as of the beginning of the period (in shares) at Jun. 30, 2025		109,501,876
Balance as of the beginning of the period at Jun. 30, 2025		$ 0	$ (5,483)	419	11,221	(903)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock option exercises, shares		0
Stock option exercises		$ 0
Stock awards (in shares)		2,479
Stock awards		$ 0
Issuance of treasury stock under stock plans (in shares)			0
Issuance of treasury stock under stock plans			$ 0
Stock-based compensation, net of tax				6
Net earnings (loss) attributable to Celanese Corporation	(1,357)				(1,357)
Common stock dividends					(3)
Other comprehensive income (loss), net of tax	55					54
Balance as of the end of the period (in shares) at Sep. 30, 2025		109,504,355
Balance as of the end of the period at Sep. 30, 2025	3,954	$ 0	$ (5,483)	425	9,861	(849)
Balance as of the end of the period (in shares) at Sep. 30, 2025			61,412,585
Balance as of the beginning of the period, noncontrolling interest at Jun. 30, 2025	428
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss) attributable to noncontrolling interests	4
Other comprehensive income (loss), net of tax	1
Distributions/dividends to noncontrolling interests	(8)
Balance as of the end of the period, noncontrolling interest at Sep. 30, 2025	425
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total equity	4,379
Total equity	4,472					(776)
Balance as of the beginning of the period (in shares) at Dec. 31, 2025			61,348,064
Balance as of the beginning of the period (in shares) at Dec. 31, 2025		109,570,157
Balance as of the beginning of the period at Dec. 31, 2025	4,049	$ 0	$ (5,482)	431	9,876	(776)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock option exercises, shares		5,506
Stock option exercises		$ 0
Stock awards (in shares)		176,524
Stock awards		$ 0
Issuance of treasury stock under stock plans (in shares)			(60,765)
Issuance of treasury stock under stock plans			$ 2
Stock-based compensation, net of tax				28
Net earnings (loss) attributable to Celanese Corporation	243				243
Common stock dividends					(10)
Other comprehensive income (loss), net of tax	(90)					(96)
Balance as of the end of the period (in shares) at Sep. 30, 2026		109,752,187
Balance as of the end of the period at Sep. 30, 2026	4,216	$ 0	$ (5,480)	459	10,109	(872)
Balance as of the end of the period (in shares) at Sep. 30, 2026			61,287,299
Balance as of the beginning of the period, noncontrolling interest at Dec. 31, 2025	423
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss) attributable to noncontrolling interests	12
Other comprehensive income (loss), net of tax	6
Distributions/dividends to noncontrolling interests	(22)
Balance as of the end of the period, noncontrolling interest at Sep. 30, 2026	419
Balance as of the beginning of the period (in shares) at Jun. 30, 2026			61,287,299
Balance as of the beginning of the period (in shares) at Jun. 30, 2026		109,748,805
Balance as of the beginning of the period at Jun. 30, 2026		$ 0	$ (5,480)	450	10,039	(842)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock option exercises, shares		0
Stock option exercises		$ 0
Stock awards (in shares)		3,382
Stock awards		$ 0
Issuance of treasury stock under stock plans (in shares)			0
Issuance of treasury stock under stock plans			$ 0
Stock-based compensation, net of tax				9
Net earnings (loss) attributable to Celanese Corporation	74				74
Common stock dividends					(4)
Other comprehensive income (loss), net of tax	(28)					(30)
Balance as of the end of the period (in shares) at Sep. 30, 2026		109,752,187
Balance as of the end of the period at Sep. 30, 2026	4,216	$ 0	$ (5,480)	$ 459	$ 10,109	(872)
Balance as of the end of the period (in shares) at Sep. 30, 2026			61,287,299
Balance as of the beginning of the period, noncontrolling interest at Jun. 30, 2026	421
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss) attributable to noncontrolling interests	4
Other comprehensive income (loss), net of tax	2
Distributions/dividends to noncontrolling interests	(8)
Balance as of the end of the period, noncontrolling interest at Sep. 30, 2026	419
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total equity	$ 4,635					$ (872)