Leases - Lease Costs (Details) - USD ($) $ in Millions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2019 |
Dec. 31, 2018 |
|
| Lessee, Lease, Description [Line Items] | ||
| Finance lease cost, amortization of leased assets | $ 110 | $ 100 |
| Finance lease cost, interest of lease liabilities | 29 | 22 |
| Operating lease cost | 1,013 | 994 |
| Short-term lease cost | 500 | 458 |
| Variable lease cost | 1,456 | 1,427 |
| Total lease cost | 3,108 | 3,001 |
| Regional carrier | ||
| Lessee, Lease, Description [Line Items] | ||
| Operating lease cost | 174 | 150 |
| Short-term lease cost | 18 | |
| Variable lease cost | $ 64 | $ 48 |