Pension and Postretirement Plans (Summary of Amounts Recognized in the Consolidated Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Noncurrent liabilities	$ (867)	$ (884)
Pension Benefits | United States
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	0	0
Current liabilities	(25)	(25)
Noncurrent liabilities	(328)	(267)
Total recognized	(353)	(292)
Pension Benefits | Int’l.
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	78	0
Current liabilities	0	0
Noncurrent liabilities	(183)	(237)
Total recognized	(105)	(237)
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	0	0
Current liabilities	(16)	(16)
Noncurrent liabilities	(204)	(216)
Total recognized	$ (220)	$ (232)