Retirement-Related Benefits - All Retirement Plans Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Retirement Benefits [Abstract]
Defined benefit and contribution pension plans — cost	$ 250	$ 6,319	$ 791	$ 7,252
Nonpension postretirement plans — cost	33	31	98	97
Total	$ 283	$ 6,350	$ 888	$ 7,350
Year-to-year percent change, defined benefit and contribution pension plans cost (as a percent)	(96.00%)		(89.10%)
Year-to-year percent change, nonpension postretirement plans cost (as a percent)	5.30%		0.40%
Year-to-year percent change, total (as a percent)	(95.50%)		(87.90%)