Pension and Other Benefit Programs - Benefit Obligations and Fair Value of Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in benefit obligation:
Benefit obligation at beginning of year	$ 853	$ 861
Interest cost	27	27	$ 34
Actuarial loss	44	14
Benefits paid	(49)	(49)
Benefit obligation at year end	875	853	861
Change in plan assets:
Fair value of plan assets at beginning of year	681	666
Actual return on plan assets	101	54
Contributions	136	10	10
Benefits paid	(49)	(49)
Fair value of plan assets at end of year	869	681	$ 666
Funded status	(6)	(172)
Accumulated benefit obligation	875	853
Amounts recognized in the accompanying consolidated balance sheets:
Accrued employee benefits	(243)	(430)
Accrued Employee Benefits
Amounts recognized in the accompanying consolidated balance sheets:
Accrued employee benefits	$ (6)	$ (172)