Pension and Other Benefit Programs - Benefit Obligation, Benefits Paid During the Period, Accrued Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in benefit obligation:
Benefit obligation at beginning of year	$ 791	$ 875	$ 853
Interest cost	26	27	$ 27
Actuarial (gain) loss	(61)	44
Benefits paid	(49)	(49)
Amounts recognized in the accompanying consolidated balance sheets:
Accrued employee benefits	(204)	(243)
Post-retirement Benefit Plans
Change in benefit obligation:
Benefit obligation at beginning of year	154	179
Interest cost	5	5
Actuarial (gain) loss	(19)	(16)
Employee contributions	3	3
Benefits paid	(13)	(14)
Amounts recognized in the accompanying consolidated balance sheets:
Other current liabilities	(10)	(11)
Accrued employee benefits	$ (144)	$ (168)