Retirement Benefits - Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Worldwide OPEB
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	$ 12	$ 11	$ 24	$ 23
Interest cost	32	41	64	84
Expected return on assets	0	0	0	0
Amortization of prior service costs/(credits)	(3)	(4)	(6)	(8)
Net remeasurement (gain)/loss	0	0	0	58
Defined Benefit Plan, Other Cost (Credit)	0	1	0	0
Settlements and curtailments	0	0	0	(2)
Net periodic benefit cost/(income)	41	49	82	155
Pension Plan | Global Redesign
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Net periodic benefit cost/(income)	46	51	84	75
Foreign Plan | Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	139	127	283	258
Interest cost	109	130	208	263
Expected return on assets	(284)	(254)	(569)	(521)
Amortization of prior service costs/(credits)	7	8	12	17
Net remeasurement (gain)/loss	(81)	(152)	(565)	(232)
Defined Benefit Plan, Other Cost (Credit)	47	33	84	57
Settlements and curtailments	(1)	17	0	18
Net periodic benefit cost/(income)	(64)	(91)	(547)	(140)
UNITED STATES | Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	127	130	265	260
Interest cost	239	323	462	646
Expected return on assets	(664)	(699)	(1,366)	(1,398)
Amortization of prior service costs/(credits)	0	1	1	2
Net remeasurement (gain)/loss	(182)	4	241	4
Defined Benefit Plan, Other Cost (Credit)	3	3	5	13
Settlements and curtailments	10	4	49	4
Net periodic benefit cost/(income)	$ (467)	$ (234)	$ (343)	$ (469)