Retirement-Related Benefits - Cost of Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
U.S. Plans | Pension Plan
Cost/(Income) of Pension Plans
Service cost	$ 86	$ 88	$ 173	$ 176
Interest cost	180	187	359	374
Expected return on plan assets	(266)	(268)	(532)	(536)
Amortization of prior service costs/(credits)	0	0	0	0
Recognized actuarial losses	122	70	243	140
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	122	77	244	154
Cost of defined contribution plans	16	17	31	30
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	138	93	274	184
U.S. Plans | Other Postretirement Benefits Plan
Cost/(Income) of Pension Plans
Service cost	0	0	1	1
Interest cost	25	28	50	57
Expected return on plan assets	0	0	0	0
Amortization of prior service costs/(credits)	(7)	(7)	(15)	(15)
Recognized actuarial losses	1	0	1	0
Total net periodic pension (income)/cost of defined benefit plans	19	22	38	43
Non-U.S. Plans | Pension Plan
Cost/(Income) of Pension Plans
Service cost	46	44	89	85
Interest cost	288	267	579	518
Expected return on plan assets	(361)	(369)	(724)	(715)
Amortization of prior service costs/(credits)	16	6	32	11
Recognized actuarial losses	75	87	151	169
Curtailments and settlements	3	5	4	7
Multi-employer plans	4	3	7	6
Other costs/(credits)	9	10	20	18
Total net periodic pension (income)/cost of defined benefit plans	80	52	157	99
Cost of defined contribution plans	109	103	212	199
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	189	155	369	298
Non-U.S. Plans | Other Postretirement Benefits Plan
Cost/(Income) of Pension Plans
Service cost	0	0	1	1
Interest cost	12	10	23	21
Expected return on plan assets	0	0	0	(1)
Amortization of prior service costs/(credits)	0	0	0	0
Recognized actuarial losses	0	0	0	0
Total net periodic pension (income)/cost of defined benefit plans	$ 12	$ 11	$ 24	$ 22