Retirement-Related Benefits - All Retirement Plans Cost (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2019 |
Sep. 30, 2018 |
Sep. 30, 2019 |
Sep. 30, 2018 |
|
| Retirement-Related Benefits | ||||
| Defined benefit and contribution pension plans - cost | $ 459 | $ 705 | $ 1,337 | $ 2,152 |
| Nonpension postretirement plans - cost | 53 | 49 | 160 | 149 |
| Total | $ 512 | $ 754 | $ 1,497 | $ 2,300 |
| Year-to-year percent change, defined benefit and contribution pension plans cost (as a percent) | (34.90%) | (37.80%) | ||
| Year-to-year percent change, nonpension postretirement plans cost (as a percent) | 8.60% | 7.40% | ||
| Year-to-year percent change, total (as a percent) | (32.10%) | (34.90%) | ||