Pension and Postretirement Benefit Plans and Defined Contribution Plans - Pension Plans in Excess of Plan Assets (Details) - USD ($) $ in Millions |
Dec. 31, 2020 |
Dec. 31, 2019 |
|---|---|---|
| US [Member] | Pension Plan [Member] | Qualified Plan [Member] | ||
| Pension plans with an ABO in excess of plan assets: | ||
| Fair value of plan assets | $ 16,094 | $ 14,586 |
| ABO | 16,940 | 16,535 |
| Pension plans with a PBO in excess of plan assets: | ||
| Fair value of plan assets | 16,094 | 14,586 |
| PBO | 16,940 | 16,535 |
| US [Member] | U.S. Supplemental (Non-Qualified) Pension Plans [Member] | Non-Qualified Plan [Member] | ||
| Pension plans with an ABO in excess of plan assets: | ||
| ABO | 1,366 | 1,351 |
| Pension plans with a PBO in excess of plan assets: | ||
| PBO | 1,366 | 1,351 |
| International [Member] | Pension Plan [Member] | ||
| Pension plans with an ABO in excess of plan assets: | ||
| Fair value of plan assets | 6,674 | 5,843 |
| ABO | 8,961 | 7,960 |
| Pension plans with a PBO in excess of plan assets: | ||
| Fair value of plan assets | 6,735 | 5,947 |
| PBO | $ 9,447 | $ 8,503 |