Fair Value Measurements (Details) - Financial Instruments - USD ($) $ in Millions |
Mar. 31, 2020 |
Dec. 31, 2019 |
|---|---|---|
| Financial Instruments | ||
| Short-term securities | $ 4,033 | $ 4,943 |
| Carrying Value [Member] | ||
| Financial Instruments | ||
| Short-term securities | 4,033 | 4,943 |
| Debt | 6,459 | 6,458 |
| Commercial paper | 100 | 100 |
| Fair Value [Member] | ||
| Financial Instruments | ||
| Short-term securities | 4,033 | 4,943 |
| Debt | 8,026 | 8,049 |
| Commercial paper | 100 | 100 |
| Fair Value [Member] | Level 1 [Member] | ||
| Financial Instruments | ||
| Short-term securities | 906 | 685 |
| Debt | 0 | 0 |
| Commercial paper | 0 | 0 |
| Fair Value [Member] | Level 2 [Member] | ||
| Financial Instruments | ||
| Short-term securities | 3,076 | 4,204 |
| Debt | 8,026 | 8,049 |
| Commercial paper | 100 | 100 |
| Fair Value [Member] | Level 3 [Member] | ||
| Financial Instruments | ||
| Short-term securities | 51 | 54 |
| Debt | 0 | 0 |
| Commercial paper | $ 0 | $ 0 |