Retirement-Related Benefits - All Retirement Plans Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Retirement Benefits [Abstract]
Defined benefit pension and defined contribution pension plans — cost	$ 320	$ 259	$ 643	$ 541
Nonpension postretirement plans — cost	30	33	60	65
Total	$ 350	$ 292	$ 704	$ 606
Year-to-year percent change, Defined benefit pension and defined contribution plans — cost (as a percent)	23.60%		19.00%
Year-to-year percent change, Nonpension postretirement plans — cost (as a percent)	(8.10%)		(7.10%)
Year-to-year percent change, Total (as a percent)	20.00%		16.20%