Retirement-Related Benefits - All Retirement Plans Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Retirement-Related Benefits
Defined benefit and contribution pension plans - cost	$ 596	$ 441	$ 1,179	$ 878
Nonpension postretirement plans - cost	50	53	102	107
Total	$ 645	$ 494	$ 1,281	$ 985
Year-to-year percent change, defined benefit and contribution pension plans cost (as a percent)	34.90%		34.30%
Year-to-year percent change, nonpension postretirement plans cost (as a percent)	(5.60%)		(4.80%)
Year-to-year percent change, total (as a percent)	30.60%		30.00%