Retirement-Related Benefits - Cost of Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Cost/(Income) of Pension Plans
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	$ 3,024	$ 250	$ 3,667	$ 791
U.S. Plans | Pension Plan
Cost/(Income) of Pension Plans
Service cost	98	0	295	0
Interest cost	228	272	735	817
Expected return on plan assets	(313)	(382)	(994)	(1,146)
Amortization of prior service costs/(credits)	0	0	0	0
Recognized actuarial losses	113	27	370	82
Curtailments and settlements	2,725	0	2,725	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	2,851	(82)	3,131	(247)
Cost of defined contribution plans	15	150	42	473
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	2,866	68	3,173	226
U.S. Plans | Other Postretirement Benefits Plan
Cost/(Income) of Pension Plans
Service cost	1	1	2	3
Interest cost	27	29	80	88
Expected return on plan assets	0	0	0	0
Amortization of prior service costs/(credits)	(7)	(7)	(22)	(22)
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	59	69
Non-U.S. Plans | Pension Plan
Cost/(Income) of Pension Plans
Service cost	43	44	128	133
Interest cost	271	293	803	873
Expected return on plan assets	(395)	(363)	(1,168)	(1,081)
Amortization of prior service costs/(credits)	6	5	17	15
Recognized actuarial losses	131	99	389	302
Curtailments and settlements	2	2	7	7
Multi-employer plans	3	4	10	10
Other costs/(credits)	0	3	20	21
Total net periodic pension (income)/cost of defined benefit plans	62	88	206	281
Cost of defined contribution plans	95	95	288	283
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	158	182	494	565
Non-U.S. Plans | Other Postretirement Benefits Plan
Cost/(Income) of Pension Plans
Service cost	1	1	2	2
Interest cost	10	10	31	29
Expected return on plan assets	0	(1)	(1)	(2)
Amortization of prior service costs/(credits)	0	0	0	0
Recognized actuarial losses	0	0	(1)	(1)
Curtailments and settlements	0	0	0	0
Total net periodic pension (income)/cost of defined benefit plans	$ 10	$ 10	$ 30	$ 28