Retirement-Related Benefits - All Retirement Plans Cost (Details) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2021 |
Mar. 31, 2020 |
|
| Retirement-Related Benefits | ||
| Defined benefit and contribution pension plans - cost | $ 672 | $ 584 |
| Nonpension postretirement plans - cost | 44 | 52 |
| Total | $ 717 | $ 636 |
| Year-to-year percent change, defined benefit and contribution pension plans cost (as a percent) | 15.20% | |
| Year-to-year percent change, nonpension postretirement plans cost (as a percent) | (14.50%) | |
| Year-to-year percent change, total (as a percent) | 12.80% | |