Fair Value Measurements - Fair Value Measurements on a Recurring Basis (Details) - USD ($)
$ in Millions |
Dec. 31, 2019 |
Dec. 31, 2018 |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Long-term investments |
$ 1,099
|
$ 1,090
|
| Recurring |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Cash equivalents |
586
|
1,222
|
| Restricted cash equivalents |
847
|
1,183
|
| Long-term investments |
1,099
|
1,090
|
| Recurring | U.S. government securities |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Short-term investments |
|
50
|
| Recurring | Asset- and mortgage-backed securities |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Short-term investments |
|
36
|
| Recurring | Corporate obligations |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Short-term investments |
|
90
|
| Recurring | Other fixed income securities |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Short-term investments |
|
27
|
| Recurring | Fuel hedge contracts |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Hedge derivatives, net |
1
|
15
|
| Recurring | Interest rate contracts |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Hedge derivatives, net |
61
|
1
|
| Recurring | Foreign currency exchange contracts |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Hedge derivatives, net |
6
|
(3)
|
| Recurring | Level 1 |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Cash equivalents |
586
|
1,222
|
| Restricted cash equivalents |
847
|
1,183
|
| Long-term investments |
881
|
880
|
| Recurring | Level 1 | U.S. government securities |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Short-term investments |
|
45
|
| Recurring | Level 1 | Asset- and mortgage-backed securities |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Short-term investments |
|
0
|
| Recurring | Level 1 | Corporate obligations |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Short-term investments |
|
0
|
| Recurring | Level 1 | Other fixed income securities |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Short-term investments |
|
0
|
| Recurring | Level 1 | Fuel hedge contracts |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Hedge derivatives, net |
(1)
|
20
|
| Recurring | Level 1 | Interest rate contracts |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Hedge derivatives, net |
0
|
0
|
| Recurring | Level 1 | Foreign currency exchange contracts |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Hedge derivatives, net |
0
|
0
|
| Recurring | Level 2 |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Cash equivalents |
0
|
0
|
| Restricted cash equivalents |
0
|
0
|
| Long-term investments |
218
|
210
|
| Recurring | Level 2 | U.S. government securities |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Short-term investments |
|
5
|
| Recurring | Level 2 | Asset- and mortgage-backed securities |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Short-term investments |
|
36
|
| Recurring | Level 2 | Corporate obligations |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Short-term investments |
|
90
|
| Recurring | Level 2 | Other fixed income securities |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Short-term investments |
|
27
|
| Recurring | Level 2 | Fuel hedge contracts |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Hedge derivatives, net |
2
|
(5)
|
| Recurring | Level 2 | Interest rate contracts |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Hedge derivatives, net |
61
|
1
|
| Recurring | Level 2 | Foreign currency exchange contracts |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |
|
|
| Hedge derivatives, net |
$ 6
|
$ (3)
|