Retirement-Related Benefits - Contributions (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Retirement-Related Benefits
Employer contributions	$ 172	$ 217
Contributions by employer - Noncash	129	70
Nonpension Postretirement Benefit Plans | Non-U.S. DB plans
Retirement-Related Benefits
Contributions by employer - Noncash	150	185
U.S.
Retirement-Related Benefits
Employer contributions	106	136
Non-U.S.
Retirement-Related Benefits
Employer contributions	$ 66	$ 82