Retirement-Related Benefits - Cost of Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Cost/(Income) of Pension Plans
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	$ 233	$ 3,024	$ 714	$ 3,667
U.S. Plans | Pension Plan
Cost/(Income) of Pension Plans
Service cost	88	98	264	295
Interest cost	187	228	561	735
Expected return on plan assets	(268)	(313)	(804)	(994)
Amortization of prior service costs/(credits)	0	0	0	0
Recognized actuarial losses	70	113	210	370
Curtailments and settlements	0	2,725	0	2,725
Multi-employer plans	0	0	0	0
Other costs/(credits)	0	0	0	0
Total net periodic pension (income)/cost of defined benefit plans	77	2,851	230	3,131
Cost of defined contribution plans	16	15	46	42
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	93	2,866	276	3,173
U.S. Plans | Other Postretirement Benefits Plan
Cost/(Income) of Pension Plans
Service cost	0	1	1	2
Interest cost	28	27	85	80
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	22	20	65	59
Non-U.S. Plans | Pension Plan
Cost/(Income) of Pension Plans
Service cost	45	43	130	128
Interest cost	273	271	790	803
Expected return on plan assets	(376)	(395)	(1,091)	(1,168)
Amortization of prior service costs/(credits)	6	6	17	17
Recognized actuarial losses	88	131	257	389
Curtailments and settlements	2	2	8	7
Multi-employer plans	3	3	10	10
Other costs/(credits)	0	0	18	20
Total net periodic pension (income)/cost of defined benefit plans	40	62	139	206
Cost of defined contribution plans	100	95	299	288
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	140	158	438	494
Non-U.S. Plans | Other Postretirement Benefits Plan
Cost/(Income) of Pension Plans
Service cost	1	1	1	2
Interest cost	11	10	31	31
Expected return on plan assets	0	0	(1)	(1)
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	$ 11	$ 10	$ 33	$ 30