Retirement-Related Benefits - Contributions (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Retirement-Related Benefits
Employer contributions	$ 237	$ 311
Pension Plans, Including Multi-employer Plans
Retirement-Related Benefits
Contributions by employer - Noncash	249	160
Nonpension Postretirement Plans | Non-U.S. DB plans
Retirement-Related Benefits
Contributions by employer - Noncash	235	250
U.S.
Retirement-Related Benefits
Employer contributions	191	200
Non-U.S.
Retirement-Related Benefits
Employer contributions	$ 46	$ 111