Restructuring Costs (Details) $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended	18 Months Ended	34 Months Ended
	Mar. 31, 2017	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)
Restructuring and Related Cost [Abstract]
Restructuring costs		$ 114	$ 169	$ 183	$ 921
Employee Separation Charges [Roll Forward]
Liability balance at beginning of period				249	147	$ 147	$ 147
Increase in liability (separation charges)				78		525
Reduction in liability (payments)				(150)		(423)
Liability balance at end of period		177		177		249	177	$ 177
September 2015 announcement
Restructuring and Related Cost [Abstract]
Restructuring costs				70				1,737
Estimated restructuring costs		150		150			150	150
Gosselies closure announcement
Restructuring and Related Cost [Abstract]
Restructuring costs				10		$ 653	663
Estimated restructuring costs		675		675			$ 675	$ 675
Positions eliminated	2,000
Employee separations | Other Operating Income (Expense)
Restructuring and Related Cost [Abstract]
Restructuring costs		45	42	78	506
Contract terminations | Other Operating Income (Expense)
Restructuring and Related Cost [Abstract]
Restructuring costs		0	17	0	26
Long-lived asset impairments | Other Operating Income (Expense)
Restructuring and Related Cost [Abstract]
Restructuring costs		30	63	30	275
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		$ 39	$ 47	$ 75	$ 85