Retirement-Related Benefits - Contributions (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Retirement-Related Benefits
Employer contributions	$ 217	$ 288
Pension Plans, Including Multi-employer Plans
Retirement-Related Benefits
Contributions by employer - Noncash	255	256
U.S.
Retirement-Related Benefits
Employer contributions	136	194
Non-U.S.
Retirement-Related Benefits
Employer contributions	$ 82	$ 94