Retirement-Related Benefits - All Retirement Plans Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Retirement-Related Benefits
Defined benefit and contribution pension plans - cost	$ 441	$ 709	$ 878	$ 1,447
Nonpension postretirement plans - cost	53	49	107	100
Total	$ 494	$ 758	$ 985	$ 1,546
Year-to-year percent change, defined benefit and contribution pension plans cost (as a percent)	(37.70%)		(39.30%)
Year-to-year percent change, nonpension postretirement plans cost (as a percent)	7.30%		6.90%
Year-to-year percent change, total (as a percent)	(34.80%)		(36.30%)