Pension and Other Benefit Programs - Fair Value Of Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	$ 869	$ 681	$ 666
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	499	127
Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	367	551
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	3	3
Cash
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	164	21
Cash | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	164	21
Cash | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	0	0
Cash | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	0	0
U.S. large-cap
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	30	247
U.S. large-cap | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	0	0
U.S. large-cap | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	30	247
U.S. large-cap | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	0	0
U.S. small-cap
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	8	68
U.S. small-cap | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	0	0
U.S. small-cap | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	8	68
U.S. small-cap | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	0	0
International
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	15	134
International | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	0	0
International | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	15	134
International | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	0	0
Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	652	211
Fixed income securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	335	106
Fixed income securities | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	314	102
Fixed income securities | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	$ 3	$ 3