Retirement-Related Benefits - Contributions, Defined Benefit Pension Plans (Details) - USD ($) $ in Millions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2020 |
Dec. 31, 2019 |
|
| Pension Contributions | ||
| Contributions by employer - Noncash | $ 288 | $ 180 |
| Pension Plans, including Multi-employer Plans, and Nonpension Postretirement Benefits Plans | Non-U.S. | ||
| Pension Contributions | ||
| Estimated cash contributions to the defined benefit plans in next fiscal year | $ 300 | |