Retirement-Related Benefits - Cost of Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Cost/(Income) of Pension Plans
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	$ 320	$ 259	$ 643	$ 541
U.S. Plans | Pension Plan
Cost/(Income) of Pension Plans
Service cost	98	0	197	0
Interest cost	254	272	508	545
Expected return on plan assets	(340)	(382)	(681)	(764)
Amortization of prior service costs/(credits)	0	0	0	0
Recognized actuarial losses	129	27	257	55
Curtailments and settlements	0	0	0	0
Multi-employer plans	0	0	0	0
Other costs/(credits)	0	0	0	0
Total net periodic pension (income)/cost of defined benefit plans	140	(82)	280	(165)
Cost of defined contribution plans	15	151	27	323
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	155	69	307	158
U.S. Plans | Other Postretirement Benefits Plan
Cost/(Income) of Pension Plans
Service cost	1	1	1	2
Interest cost	27	29	53	58
Expected return on plan assets	0	0	0	0
Amortization of prior service costs/(credits)	(7)	(7)	(15)	(15)
Recognized actuarial losses	0	0	0	0
Curtailments and settlements	0	0	0	0
Total net periodic pension (income)/cost of defined benefit plans	20	23	40	46
Non-U.S. Plans | Pension Plan
Cost/(Income) of Pension Plans
Service cost	41	44	85	88
Interest cost	264	292	532	580
Expected return on plan assets	(384)	(362)	(773)	(718)
Amortization of prior service costs/(credits)	5	5	11	10
Recognized actuarial losses	128	101	258	203
Curtailments and settlements	2	6	4	5
Multi-employer plans	3	3	6	6
Other costs/(credits)	12	10	20	19
Total net periodic pension (income)/cost of defined benefit plans	71	99	143	194
Cost of defined contribution plans	94	91	193	188
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	165	190	336	382
Non-U.S. Plans | Other Postretirement Benefits Plan
Cost/(Income) of Pension Plans
Service cost	1	1	1	1
Interest cost	10	10	21	19
Expected return on plan assets	0	(1)	(1)	(1)
Amortization of prior service costs/(credits)	0	0	0	0
Recognized actuarial losses	0	0	0	(1)
Curtailments and settlements	0	0	0	0
Total net periodic pension (income)/cost of defined benefit plans	$ 10	$ 10	$ 21	$ 19