Retirement-Related Benefits - Cost of Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
U.S. Plans | Pension Plan
Cost/(Income) of Pension Plans
Service cost	$ 87	$ 88	$ 259	$ 264
Interest cost	180	187	539	561
Expected return on plan assets	(266)	(268)	(798)	(804)
Amortization of prior service costs/(credits)	0	0	0	0
Recognized actuarial losses	122	70	365	210
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	366	230
Cost of defined contribution plans	15	16	45	46
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	136	93	411	276
U.S. Plans | Other Postretirement Benefits Plan
Cost/(Income) of Pension Plans
Service cost	0	0	1	1
Interest cost	25	28	75	85
Expected return on plan assets	0	0	0	0
Amortization of prior service costs/(credits)	(7)	(7)	(22)	(22)
Recognized actuarial losses	1	0	2	0
Total net periodic pension (income)/cost of defined benefit plans	19	22	56	65
Non-U.S. Plans | Pension Plan
Cost/(Income) of Pension Plans
Service cost	43	45	132	130
Interest cost	286	273	865	790
Expected return on plan assets	(359)	(376)	(1,083)	(1,091)
Amortization of prior service costs/(credits)	16	6	48	17
Recognized actuarial losses	74	88	225	257
Curtailments and settlements	2	2	7	8
Multi-employer plans	3	3	10	10
Other costs/(credits)	6	0	26	18
Total net periodic pension (income)/cost of defined benefit plans	71	40	229	139
Cost of defined contribution plans	98	100	310	299
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	169	140	538	438
Non-U.S. Plans | Other Postretirement Benefits Plan
Cost/(Income) of Pension Plans
Service cost	0	1	1	1
Interest cost	12	11	35	31
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	1
Total net periodic pension (income)/cost of defined benefit plans	$ 12	$ 11	$ 36	$ 33