Retirement-Related Benefits - All Retirement Plans Cost (Details) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2019 |
Mar. 31, 2018 |
|
| Retirement-Related Benefits | ||
| Defined benefit and contribution pension plans - cost | $ 437 | $ 738 |
| Nonpension postretirement plans - cost | 54 | 51 |
| Total | $ 491 | $ 788 |
| Year-to-year percent change, defined benefit and contribution pension plans cost (as a percent) | (40.80%) | |
| Year-to-year percent change, nonpension postretirement plans cost (as a percent) | 6.40% | |
| Year-to-year percent change, total (as a percent) | (37.70%) | |