Restructuring Costs (Details) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended	21 Months Ended	37 Months Ended
	Mar. 31, 2017	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)
Restructuring and Related Cost [Abstract]
Restructuring costs		$ 110	$ 90	$ 293	$ 1,011
Employee Separation Charges [Roll Forward]
Liability balance at beginning of period				249	147	$ 147	$ 147
Increase in liability (separation charges)				121		525
Reduction in liability (payments)				(233)		(423)
Liability balance at end of period		137		137		249	137	$ 137
September 2015 announcement
Restructuring and Related Cost [Abstract]
Restructuring costs				109				1,776
Estimated restructuring costs		50		50			50	50
Gosselies closure announcement
Restructuring and Related Cost [Abstract]
Restructuring costs				11	649	$ 653	664
Estimated restructuring costs		675		675			$ 675	$ 675
Positions eliminated	2,000
Employee separations | Other Operating Income (Expense)
Restructuring and Related Cost [Abstract]
Restructuring costs		44	8	121	514
Contract terminations | Other Operating Income (Expense)
Restructuring and Related Cost [Abstract]
Restructuring costs		0	6	0	32
Long-lived asset impairments | Other Operating Income (Expense)
Restructuring and Related Cost [Abstract]
Restructuring costs		18	31	49	306
Defined benefit retirement plan curtailments and termination benefits | Other Operating Income (Expense)
Restructuring and Related Cost [Abstract]
Restructuring costs				0	29
Other | Other Operating Income (Expense)
Restructuring and Related Cost [Abstract]
Restructuring costs		$ 48	$ 45	$ 123	$ 130