Retirement-Related Benefits - Cost of Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Cost/(Income) of Pension Plans
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	$ 233	$ 323
U.S. Plans | Pension Plan
Cost/(Income) of Pension Plans
Service cost	88	98
Interest cost	187	254
Expected return on plan assets	(268)	(340)
Amortization of prior service costs/(credits)	0	0
Recognized actuarial losses	70	129
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	77	140
Cost of defined contribution plans	14	12
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	90	152
U.S. Plans | Other Postretirement Benefits Plan
Cost/(Income) of Pension Plans
Service cost	0	1
Interest cost	28	27
Expected return on plan assets	0	0
Amortization of prior service costs/(credits)	(7)	(7)
Recognized actuarial losses	0	0
Curtailments and settlements	0	0
Total net periodic pension (income)/cost of defined benefit plans	22	20
Non-U.S. Plans | Pension Plan
Cost/(Income) of Pension Plans
Service cost	41	44
Interest cost	251	267
Expected return on plan assets	(345)	(389)
Amortization of prior service costs/(credits)	5	5
Recognized actuarial losses	81	130
Curtailments and settlements	2	2
Multi-employer plans	3	4
Other costs/(credits)	8	8
Total net periodic pension (income)/cost of defined benefit plans	47	72
Cost of defined contribution plans	96	99
Total defined benefit pension and defined contribution plans cost recognized in the Consolidated Income Statement	143	171
Non-U.S. Plans | Other Postretirement Benefits Plan
Cost/(Income) of Pension Plans
Service cost	0	1
Interest cost	10	11
Expected return on plan assets	0	0
Amortization of prior service costs/(credits)	0	0
Recognized actuarial losses	0	0
Curtailments and settlements	0	0
Total net periodic pension (income)/cost of defined benefit plans	$ 11	$ 11