Restructuring Costs (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended	43 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Mar. 31, 2019
Restructuring and Related Cost [Abstract]
Restructuring costs	$ 48	$ 69
Employee Separation Charges [Roll Forward]
Liability balance at beginning of period	85	249	$ 249
Increase in liability (separation charges)	15		112
Reduction in liability (payments)	(41)		(276)
Liability balance at end of period	59		$ 85	$ 59
September 2015 announcement [Member]
Restructuring and Related Cost [Abstract]
Restructuring costs	4			1,792
Estimated restructuring costs	40			$ 40
Employee separations | Other Operating Income (Expense)
Restructuring and Related Cost [Abstract]
Restructuring costs	15	33
Long-lived asset impairments | Other Operating Income (Expense)
Restructuring and Related Cost [Abstract]
Restructuring costs	7	0
Other | Other Operating Income (Expense)
Restructuring and Related Cost [Abstract]
Restructuring costs	$ 26	$ 36