Unaudited Interim Consolidated Statement Equity - USD ($) $ in Millions	Total	Common Stock	Treasury Stock, Common	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)		75,847
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				4
Net earnings (loss) attributable to Celanese Corporation	$ (24)				(24)
Common stock dividends					(3)
Other comprehensive income (loss), net of tax	31					31
Balance as of the end of the period (in shares) at Mar. 31, 2025		109,403,403
Balance as of the end of the period at Mar. 31, 2025	5,137	$ 0	$ (5,486)	413	11,027	(817)
Balance as of the end of the period (in shares) at Mar. 31, 2025			61,499,640
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	4
Other comprehensive income (loss), net of tax	0
Distributions/dividends to noncontrolling interests	(9)
Balance as of the end of the period, noncontrolling interest at Mar. 31, 2025	429
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total equity	5,566
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		4,506
Stock option exercises		$ 0
Stock awards (in shares)		86,675
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				8
Net earnings (loss) attributable to Celanese Corporation	44				44
Common stock dividends					(3)
Other comprehensive income (loss), net of tax	(33)					(35)
Balance as of the end of the period (in shares) at Mar. 31, 2026		109,661,338
Balance as of the end of the period at Mar. 31, 2026	4,063	$ 0	$ (5,482)	$ 439	$ 9,917	(811)
Balance as of the end of the period (in shares) at Mar. 31, 2026			61,348,064
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	4
Other comprehensive income (loss), net of tax	2
Distributions/dividends to noncontrolling interests	(7)
Balance as of the end of the period, noncontrolling interest at Mar. 31, 2026	422
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total equity	$ 4,485					$ (811)