Unaudited Interim Consolidated Statement Equity - USD ($) $ in Millions	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interest [Member]
Balance as of the beginning of the period, shares at Dec. 31, 2019		119,555,207	49,417,965
Total Celanese Corporation stockholders' equity at Dec. 31, 2019		$ 0	$ (3,846)	$ 254	$ 6,399	$ (300)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation, net of tax				(6)
Stock awards, shares		444,903
Stock awards		$ 0
Purchases of treasury stock, shares	(2,770,321)	(2,770,321)	2,770,321
Purchases of treasury stock, including related fees	$ (261)	$ 0	$ (261)
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture			(44,370)
Stock-based compensation, net of tax			$ 1
Net earnings (loss) attributable to Celanese Corporation	532				532
Common stock dividends					(221)
Other comprehensive income (loss), net of tax	(44)					(44)
Balance as of the end of the period, shares at Sep. 30, 2020		117,229,789	52,143,916
Stockholders' Equity Attributable to Noncontrolling Interest at Dec. 31, 2019							$ 391
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss) attributable to noncontrolling interests	6						6
(Distributions to) contributions from noncontrolling interests							(21)
Stockholders' Equity Attributable to Noncontrolling Interest at Sep. 30, 2020							376
Total Celanese Corporation stockholders' equity at Sep. 30, 2020	2,508	$ 0	$ (4,106)	248	6,710	(344)
Balance as of the end of the period at Sep. 30, 2020	2,884
Balance as of the beginning of the period, shares at Jun. 30, 2020		118,288,296	51,083,026
Total Celanese Corporation stockholders' equity at Jun. 30, 2020		$ 0	$ (3,995)	252	6,576	(346)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation, net of tax				(4)
Stock awards, shares		2,383
Stock awards		$ 0
Purchases of treasury stock, shares		(1,060,890)	1,060,890
Purchases of treasury stock, including related fees		$ 0	$ (111)
Net earnings (loss) attributable to Celanese Corporation	207				207
Common stock dividends					(73)
Other comprehensive income (loss), net of tax	2					2
Balance as of the end of the period, shares at Sep. 30, 2020		117,229,789	52,143,916
Stockholders' Equity Attributable to Noncontrolling Interest at Jun. 30, 2020							382
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss) attributable to noncontrolling interests	2						2
(Distributions to) contributions from noncontrolling interests							(8)
Stockholders' Equity Attributable to Noncontrolling Interest at Sep. 30, 2020							376
Total Celanese Corporation stockholders' equity at Sep. 30, 2020	2,508	$ 0	$ (4,106)	248	6,710	(344)
Balance as of the end of the period at Sep. 30, 2020	2,884
Balance as of the beginning of the period, shares at Dec. 31, 2020		114,168,464	55,234,515
Balance as of the beginning of the period at Dec. 31, 2020	3,895
Total Celanese Corporation stockholders' equity at Dec. 31, 2020	$ 3,526	$ 0	$ (4,494)	257	8,091	(328)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation, net of tax				56
Stock awards, shares		344,586
Stock awards		$ 0
Purchases of treasury stock, shares	(5,332,727)	(5,332,727)	5,332,727
Purchases of treasury stock, including related fees	$ (800)	$ 0	$ (800)
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture			(27,186)
Stock-based compensation, net of tax			$ 1
Net earnings (loss) attributable to Celanese Corporation	1,366				1,366
Common stock dividends					(230)
Other comprehensive income (loss), net of tax	0					0
Balance as of the end of the period, shares at Sep. 30, 2021		109,180,323	60,540,056
Stockholders' Equity Attributable to Noncontrolling Interest at Dec. 31, 2020	369						369
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss) attributable to noncontrolling interests	4						4
(Distributions to) contributions from noncontrolling interests							(21)
Stockholders' Equity Attributable to Noncontrolling Interest at Sep. 30, 2021	352						352
Total Celanese Corporation stockholders' equity at Sep. 30, 2021	3,919	$ 0	$ (5,293)	313	9,227	(328)
Balance as of the end of the period at Sep. 30, 2021	4,271
Balance as of the beginning of the period, shares at Jun. 30, 2021		111,115,442	58,601,877
Total Celanese Corporation stockholders' equity at Jun. 30, 2021		$ 0	$ (4,993)	292	8,797	(298)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation, net of tax				21
Stock awards, shares		3,060
Stock awards		$ 0
Purchases of treasury stock, shares		(1,938,179)	1,938,179
Purchases of treasury stock, including related fees		$ 0	$ (300)
Net earnings (loss) attributable to Celanese Corporation	506				506
Common stock dividends					(76)
Other comprehensive income (loss), net of tax	(30)					(30)
Balance as of the end of the period, shares at Sep. 30, 2021		109,180,323	60,540,056
Stockholders' Equity Attributable to Noncontrolling Interest at Jun. 30, 2021							359
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss) attributable to noncontrolling interests	1						1
(Distributions to) contributions from noncontrolling interests							(8)
Stockholders' Equity Attributable to Noncontrolling Interest at Sep. 30, 2021	352						$ 352
Total Celanese Corporation stockholders' equity at Sep. 30, 2021	3,919	$ 0	$ (5,293)	$ 313	$ 9,227	$ (328)
Balance as of the end of the period at Sep. 30, 2021	$ 4,271