Pension and Other Benefit Programs - Fair Value Of Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	$ 819
Fair Value Measurements	794	$ 869	$ 681
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	135
Fair Value Measurements		499
Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	677
Fair Value Measurements		367
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	7
Fair Value Measurements		3
Cash
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	8
Fair Value Measurements		164
Cash | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	8
Fair Value Measurements		164
Cash | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	0
Fair Value Measurements		0
Cash | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	0
Fair Value Measurements		0
U.S. large-cap
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	21
Fair Value Measurements		30
U.S. large-cap | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	0
Fair Value Measurements		0
U.S. large-cap | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	21
Fair Value Measurements		30
U.S. large-cap | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	0
Fair Value Measurements		0
U.S. small-cap
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	5
Fair Value Measurements		8
U.S. small-cap | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	0
Fair Value Measurements		0
U.S. small-cap | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	5
Fair Value Measurements		8
U.S. small-cap | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	0
Fair Value Measurements		0
International
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	11
Fair Value Measurements		15
International | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	0
Fair Value Measurements		0
International | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	11
Fair Value Measurements		15
International | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	0
Fair Value Measurements		0
Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	774
Fair Value Measurements		652
Fixed income securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	127
Fair Value Measurements		335
Fixed income securities | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	640
Fair Value Measurements		314
Fixed income securities | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair Value Measurements	$ 7
Fair Value Measurements		$ 3