Debt (Senior Credit Facilities Narrative) (Details) - USD ($) $ in Millions			12 Months Ended
		Sep. 26, 2016	Dec. 31, 2017	Jul. 15, 2016
Senior Unsecured Term Loan Due 2021 [Member]
Debt Instrument [Line Items]
Secured Debt	[1]			$ 500
Revolving Credit Facility [Member] | Senior Unsecured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 1,000
Proceeds from Lines of Credit			$ 528
Repayments of Lines of Credit		$ 411	$ 431

[1] The margin for borrowings under the senior unsecured term loan due 2021 was 1.5% above LIBOR at current Celanese credit ratings.