Retirement-Related Benefits - Cost of Pension Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Cost/(Income) of Pension Plans
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	$ 323	$ 281
U.S. Plans | Pension Plan
Cost/(Income) of Pension Plans
Service cost	98	0
Interest cost	254	272
Expected return on plan assets	(340)	(382)
Amortization of prior service costs/(credits)	0	0
Recognized actuarial losses	129	27
Curtailments and settlements	0	0
Multi-employer plans	0	0
Other costs/(credits)	0	0
Total net periodic pension (income)/cost of defined benefit plans	140	(82)
Cost of defined contribution plans	12	172
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	152	90
U.S. Plans | Other Postretirement Benefits Plan
Cost/(Income) of Pension Plans
Service cost	1	1
Interest cost	27	29
Expected return on plan assets	0	0
Amortization of prior service costs/(credits)	(7)	(7)
Recognized actuarial losses	0	0
Curtailments and settlements	0	0
Total net periodic pension (income)/cost of defined benefit plans	20	23
Non-U.S. Plans | Pension Plan
Cost/(Income) of Pension Plans
Service cost	44	44
Interest cost	267	288
Expected return on plan assets	(389)	(356)
Amortization of prior service costs/(credits)	5	5
Recognized actuarial losses	130	102
Curtailments and settlements	2	(1)
Multi-employer plans	4	4
Other costs/(credits)	8	9
Total net periodic pension (income)/cost of defined benefit plans	72	95
Cost of defined contribution plans	99	97
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	171	192
Non-U.S. Plans | Other Postretirement Benefits Plan
Cost/(Income) of Pension Plans
Service cost	1	1
Interest cost	11	9
Expected return on plan assets	0	(1)
Amortization of prior service costs/(credits)	0	0
Recognized actuarial losses	0	0
Curtailments and settlements	0	0
Total net periodic pension (income)/cost of defined benefit plans	$ 11	$ 9