Pension and Postretirement Benefit Plans and Defined Contribution Plans - Pension Plans in Excess of Plan Assets (Details) - USD ($) $ in Millions |
Dec. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| United States [Member] | Pension Plan [Member] | ||
| Pension plans with an ABO in excess of plan assets: | ||
| Fair value of plan assets | $ 13,051 | $ 14,284 |
| ABO | 15,141 | 16,702 |
| Pension plans with a PBO in excess of plan assets: | ||
| Fair value of plan assets | 13,051 | 14,284 |
| PBO | 15,141 | 16,702 |
| United States [Member] | U.S. Supplemental (Non-Qualified) Pension Plans [Member] | ||
| Pension plans with an ABO in excess of plan assets: | ||
| ABO | 1,280 | 1,495 |
| Pension plans with a PBO in excess of plan assets: | ||
| PBO | 1,280 | 1,495 |
| Foreign Plan [Member] | Pension Plan [Member] | ||
| Pension plans with an ABO in excess of plan assets: | ||
| Fair value of plan assets | 4,514 | 882 |
| ABO | 6,286 | 2,724 |
| Pension plans with a PBO in excess of plan assets: | ||
| Fair value of plan assets | 5,432 | 1,626 |
| PBO | $ 7,571 | $ 3,825 |