Financial Instruments - Assets and Liabilities Not Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions |
Dec. 31, 2019 |
Dec. 31, 2018 |
|---|---|---|
| Carrying Value [Member] | ||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Long-term debt, excluding the current portion | $ 35,955 | $ 32,909 |
| Estimated Fair Value [Member] | ||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Long-term debt, excluding the current portion | 40,842 | 35,260 |
| Level 2 [Member] | Estimated Fair Value [Member] | ||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Long-term debt, excluding the current portion | $ 40,842 | $ 35,260 |