Leases - Undiscounted Cash Flows (Details) - USD ($) $ in Millions |
Dec. 31, 2019 |
Dec. 31, 2018 |
|---|---|---|
| Operating Leases | ||
| 2020 | $ 1,003 | |
| 2021 | 836 | |
| 2022 | 729 | |
| 2023 | 698 | |
| 2024 | 628 | |
| Thereafter | 3,821 | |
| Total minimum lease payments | 7,715 | |
| Less: amount of lease payments representing interest | (1,620) | |
| Present value of future minimum lease payments | 6,095 | |
| Less: current obligations under leases | (801) | $ (955) |
| Noncurrent operating lease liabilities | 5,294 | 5,801 |
| Finance Leases | ||
| 2020 | 264 | |
| 2021 | 239 | |
| 2022 | 174 | |
| 2023 | 124 | |
| 2024 | 180 | |
| Thereafter | 179 | |
| Total minimum lease payments | 1,160 | |
| Less: amount of lease payments representing interest | (106) | |
| Present value of future minimum lease payments | 1,054 | |
| Less: current obligations under leases | (233) | (109) |
| Long-term lease obligations | $ 821 | $ 294 |