Retirement Benefits - Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Immediate Recognition of Actuarial Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]			Other income/(loss), net
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Expected Return (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]			Other income/(loss), net
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]			Other income/(loss), net
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Other Cost (Credit), Statement of Income or Comprehensive Income [Extensible Enumeration]			Other income/(loss), net
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Settlement and Curtailment Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]			Other income/(loss), net
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Amortization of Prior Service Cost (Credit), Statement of Income or Comprehensive Income [Extensible Enumeration]			Other income/(loss), net
Worldwide OPEB
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	$ 5	$ 10	$ 16	$ 31
Interest cost	58	36	173	110
Expected return on assets	0	0	0	0
Amortization of prior service costs/(credits)	1	(1)	3	(2)
Net remeasurement (gain)/loss	0	0	0	0
Defined Benefit Plan, Other Cost (Credit)	0	1	0	0
Settlements and curtailments	0	0	0	0
Net periodic benefit cost/(income)	64	46	192	139
Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Net remeasurement (gain)/loss	169		371
Settlements and curtailments	21		67
UNITED STATES | Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	74	125	221	375
Interest cost	413	263	1,226	790
Expected return on assets	(474)	(642)	(1,440)	(1,927)
Amortization of prior service costs/(credits)	0	0	0	1
Net remeasurement (gain)/loss	176	7	370	7
Defined Benefit Plan, Other Cost (Credit)	3	9	15	20
Settlements and curtailments	20	1	65	1
Net periodic benefit cost/(income)	212	(237)	457	(733)
Foreign Plan | Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	62	101	184	319
Interest cost	245	123	724	390
Expected return on assets	(227)	(245)	(669)	(772)
Amortization of prior service costs/(credits)	7	6	17	18
Net remeasurement (gain)/loss	(7)	0	1	16
Defined Benefit Plan, Other Cost (Credit)	57	11	118	28
Settlements and curtailments	1	0	2	0
Net periodic benefit cost/(income)	$ 138	$ (4)	$ 377	$ (1)