Retirement-Related Benefits - Cost of Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
U.S. Plans | Pension Plan
Cost/(Income) of Pension Plans
Service cost	$ 86	$ 88
Interest cost	180	187
Expected return on plan assets	(266)	(268)
Amortization of prior service costs/(credits)	0	0
Recognized actuarial losses	122	70
Curtailments and settlements	0	0
Multi-employer plans	0	0
Other costs/(credits)	0	0
Total net periodic pension (income)/cost of defined benefit plans	122	77
Cost of defined contribution plans	15	14
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	137	90
U.S. Plans | Other Postretirement Benefits Plan
Cost/(Income) of Pension Plans
Service cost	0	0
Interest cost	25	28
Expected return on plan assets	0	0
Amortization of prior service costs/(credits)	(7)	(7)
Recognized actuarial losses	1	0
Total net periodic pension (income)/cost of defined benefit plans	19	22
Non-U.S. Plans | Pension Plan
Cost/(Income) of Pension Plans
Service cost	44	41
Interest cost	290	251
Expected return on plan assets	(363)	(345)
Amortization of prior service costs/(credits)	16	5
Recognized actuarial losses	76	81
Curtailments and settlements	2	2
Multi-employer plans	3	3
Other costs/(credits)	11	8
Total net periodic pension (income)/cost of defined benefit plans	78	47
Cost of defined contribution plans	103	96
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	180	143
Non-U.S. Plans | Other Postretirement Benefits Plan
Cost/(Income) of Pension Plans
Service cost	0	0
Interest cost	12	10
Expected return on plan assets	0	0
Amortization of prior service costs/(credits)	0	0
Recognized actuarial losses	0	0
Total net periodic pension (income)/cost of defined benefit plans	$ 12	$ 11