Retirement Benefits - Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Worldwide OPEB
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 11	$ 14
Interest cost	53	49
Expected return on assets	0	0
Amortization of prior service costs/(credits)	(18)	(27)
Net remeasurement (gain)/loss	0	0
Separation programs/other	0	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	0	0
Net periodic benefit cost/(income)	46	36
Defined Benefit Plan, Estimated Future Employer Contributions To Funded Plans in Current Fiscal Year	650
Pension And Other Postretirement Expected Benefit Contributions Unfunded Plans	350
Pension and Other Postretirement Benefit Contributions and Expected Future Employer Contributions To Funded and Unfunded Plans	1,000
Payment for Pension and Other Postretirement Benefits	300
Defined Contribution Plan, Employer Discretionary Contribution Amount	140
Pension and Other Postretirement Benefit Contributions Unfunded Plans	100
Foreign Plan [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	129	152
Interest cost	176	176
Expected return on assets	(286)	(334)
Amortization of prior service costs/(credits)	8	6
Net remeasurement (gain)/loss	0	0
Separation programs/other	12	2
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	0	0
Net periodic benefit cost/(income)	39	2
UNITED STATES | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	114	136
Interest cost	409	367
Expected return on assets	(649)	(722)
Amortization of prior service costs/(credits)	22	36
Net remeasurement (gain)/loss	0	(26)
Separation programs/other	1	11
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	0	(15)
Net periodic benefit cost/(income)	$ (103)	$ (213)