Retirement-Related Benefits - Cost of Pension Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Cost/(Income) of Pension Plans
Total defined benefit and contribution pension plans cost recognized in the Consolidated Income Statement	$ 250	$ 6,319	$ 791	$ 7,252
U.S. Plans | Pension Plan
Cost/(Income) of Pension Plans
Service cost	0	0	0	0
Interest cost	272	282	817	885
Expected return on plan assets	(382)	(432)	(1,146)	(1,382)
Amortization of prior service costs/(credits)	0	2	0	6
Recognized actuarial losses	27	132	82	490
Curtailments and settlements	0	5,894	0	5,894
Multi-employer plans	0	0	0	0
Other costs/(credits)	0	0	0	0
Total net periodic pension (income)/cost of defined benefit plans	(82)	5,877	(247)	5,893
Cost of defined contribution plans	150	134	473	416
Total defined benefit and contribution pension plans cost recognized in the Consolidated Income Statement	68	6,012	226	6,309
U.S. Plans | Other Postretirement Benefits Plan
Cost/(Income) of Pension Plans
Service cost	1	1	3	4
Interest cost	29	21	88	58
Expected return on plan assets	0	0	0	0
Amortization of prior service costs/(credits)	(7)	(2)	(22)	(1)
Recognized actuarial losses	0	1	0	6
Curtailments and settlements	0	0	0	0
Total net periodic pension (income)/cost of defined benefit plans	23	21	69	67
Non-U.S. Plans | Pension Plan
Cost/(Income) of Pension Plans
Service cost	44	57	133	180
Interest cost	293	124	873	394
Expected return on plan assets	(363)	(246)	(1,081)	(778)
Amortization of prior service costs/(credits)	5	3	15	10
Recognized actuarial losses	99	247	302	784
Curtailments and settlements	2	19	7	38
Multi-employer plans	4	4	10	11
Other costs/(credits)	3	8	21	24
Total net periodic pension (income)/cost of defined benefit plans	88	216	281	663
Cost of defined contribution plans	95	91	283	280
Total defined benefit and contribution pension plans cost recognized in the Consolidated Income Statement	182	307	565	943
Non-U.S. Plans | Other Postretirement Benefits Plan
Cost/(Income) of Pension Plans
Service cost	1	1	2	2
Interest cost	10	8	29	26
Expected return on plan assets	(1)	0	(2)	(2)
Amortization of prior service costs/(credits)	0	0	0	0
Recognized actuarial losses	0	1	(1)	3
Curtailments and settlements	0	0	0	0
Total net periodic pension (income)/cost of defined benefit plans	$ 10	$ 10	$ 28	$ 30