Retirement-Related Benefits - Contributions and Direct Benefit Payments (Details) - USD ($) $ in Millions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2020 |
Dec. 31, 2019 |
|
| Defined Benefit Plan Disclosure [Line Items] | ||
| Total | $ 2,161 | $ 2,177 |
| Contributions by employer - Noncash | 288 | 180 |
| Non-U.S. DB plans | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Total | 182 | 243 |
| Multi-employer plans | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Total | 29 | 32 |
| DC plans | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Total | 1,058 | 1,040 |
| Direct Benefit Payments | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Total | 567 | 559 |
| Nonpension Postretirement Benefit Plans | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Total | 325 | 304 |
| Nonpension Postretirement Benefit Plans | Non-U.S. DB plans | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Contributions by employer - Noncash | $ 452 | $ 455 |