Retirement Benefits - Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Worldwide OPEB
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	$ 12	$ 11	$ 35	$ 33
Interest cost	43	53	127	158
Expected return on assets	0	0	0	0
Amortization of prior service costs/(credits)	(4)	(18)	(12)	(53)
Net remeasurement (gain)/loss	0	0	58	0
Separation programs/other	(1)	0	(1)	0
Settlements and curtailments	0	0	(2)	0
Net periodic benefit cost/(income)	50	46	205	138
Foreign Plan | Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	135	125	393	381
Interest cost	130	170	393	519
Expected return on assets	(272)	(277)	(793)	(844)
Amortization of prior service costs/(credits)	8	8	25	25
Net remeasurement (gain)/loss	55	43	(177)	43
Separation programs/other	66	78	123	322
Settlements and curtailments	74	(19)	92	(19)
Net periodic benefit cost/(income)	196	128	56	427
UNITED STATES | Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	130	121	390	349
Interest cost	322	381	968	1,199
Expected return on assets	(699)	(674)	(2,097)	(1,972)
Amortization of prior service costs/(credits)	1	22	3	65
Net remeasurement (gain)/loss	(1)	263	3	253
Separation programs/other	0	7	13	8
Settlements and curtailments	1	(16)	5	(66)
Net periodic benefit cost/(income)	$ (246)	$ 104	$ (715)	$ (164)