Pension and Other Benefit Programs - Effect on Accumulated Other Comprehensive Income (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unrecognized net actuarial losses (gains), after tax	$ 89
Loss recognition	4
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unrecognized net actuarial losses (gains), after tax	93
Loss recognition	4
SERP Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unrecognized net actuarial losses (gains), after tax	4
Loss recognition	0
Post-retirement Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unrecognized net actuarial losses (gains), after tax	(8)
Loss recognition	$ 0