Retirement-Related Benefits - ABO and APBO in Excess of Plan Assets (Details) - USD ($) $ in Millions |
Dec. 31, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Pension Plan | ||
| Defined Benefit Plan, Pension and Non-Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets | ||
| Plans with PBO in excess of plan assets, Benefit Obligation | $ 16,493 | $ 16,216 |
| Plans with PBO in excess of plan assets, Plan Assets | 9,423 | 8,811 |
| Plans with ABO in excess of plan assets, Benefit Obligation | 16,487 | 16,194 |
| Plans with ABO in excess of plan assets, Plan Assets | 9,417 | 8,789 |
| Plans with assets in excess of PBO, Benefit Obligation | 27,839 | 26,493 |
| Plans with assets in excess of PBO, Plan Assets | 35,383 | 33,985 |
| Other Postretirement Benefits Plan | ||
| Defined Benefit Plan, Pension and Non-Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets | ||
| Plans with ABO in excess of plan assets, Benefit Obligation | 2,771 | 2,764 |
| Plans with ABO in excess of plan assets, Plan Assets | $ 14 | $ 20 |