Retirement Benefits - Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Worldwide OPEB
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	$ 12	$ 11
Interest cost	43	53
Expected return on assets	0	0
Amortization of prior service costs/(credits)	(4)	(18)
Net remeasurement (gain)/loss	58	0
Separation programs/other	(1)	0
Settlements and curtailments	(2)	0
Net periodic benefit cost/(income)	106	46
Foreign Plan | Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	131	129
Interest cost	133	176
Expected return on assets	(267)	(286)
Amortization of prior service costs/(credits)	9	8
Net remeasurement (gain)/loss	(80)	0
Separation programs/other	24	12
Settlements and curtailments	1	0
Net periodic benefit cost/(income)	(49)	39
UNITED STATES | Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	130	114
Interest cost	323	409
Expected return on assets	(699)	(649)
Amortization of prior service costs/(credits)	1	22
Net remeasurement (gain)/loss	0	0
Separation programs/other	10	1
Settlements and curtailments	0	0
Net periodic benefit cost/(income)	$ (235)	$ (103)