Retirement-Related Benefits - All Retirement Plans Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Retirement Benefits [Abstract]
Defined benefit pension and defined contribution pension plans — cost	$ 3,024	$ 250	$ 3,667	$ 791
Nonpension postretirement plans — cost	30	33	90	98
Total	$ 3,053	$ 283	$ 3,757	888
Year-to-year percent change, Nonpension postretirement plans — cost (as a percent)	(9.40%)		(7.80%)
Pension settlement charge	$ 2,700		$ 2,725	$ 0