Retirement-Related Benefits - Changes in Benefit Obligation and Plan Assets (Details) - Pension Plan - U.S. Plans - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Aug. 31, 2024	Dec. 31, 2023
Change in benefit obligation:
Service cost	$ 98	$ 0	$ 295	$ 0
Interest cost	228	$ 272	735	$ 817
Actuarial losses/(gains)	100		300
Personal Pension Plan (PPP)
Change in benefit obligation:
Benefit obligation, balance at beginning of period			19,854
Service cost			295
Interest cost			686
Plan participants' contributions			0
Actuarial losses/(gains)			46
Benefits paid from trust			(1,073)
Direct benefit payments			0
Amendments/curtailments/settlements/other			(6,229)
Benefit obligation, balance at end of period	13,578		13,578
Change in plan assets:
Fair value of plan assets, balance at beginning of period			24,437
Actual return of plan assets			1,140
Employer contributions			0
Plan participants' contributions			0
Benefits paid from trust			(1,073)
Direct benefit payments			0
Amendments/curtailments/settlements/other			(6,229)
Fair value of plan assets, balance at end of period	18,275		18,275
Funded status	4,697		4,697
Accumulated benefit obligation	$ 13,578		$ 13,578
Discount rate					5.00%	5.00%