Retirement-Related Benefits - Nonpension Postretirement Contributions (Details) - USD ($) $ in Millions |
9 Months Ended | |
|---|---|---|
Sep. 30, 2019 |
Sep. 30, 2018 |
|
| Nonpension Postretirement Plans | U.S. | ||
| Retirement-Related Benefits | ||
| Contributions by employer - Noncash | $ 357 | $ 275 |