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Fair Value Measurements - Measured on Recurring Basis (Details) - USD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Assets |  |  |
Time Deposits |  | $ 60 |
Quoted prices in active markets for identical assets (Level 1) |  |  |
Assets |  |  |
Time Deposits |  | 0 |
Significant other observable inputs (Level 2) |  |  |
Assets |  |  |
Time Deposits |  | 60 |
Significant unobservable inputs (Level 3) |  |  |
Assets |  |  |
Time Deposits |  | 0 |
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) |  |  |
Assets |  |  |
Treasury bills |  | 1,196 | $ 1,582
Interest rate derivatives (see Note 10) |  | 0 |
Fuel derivatives: |  |  |
Other available for sale securities |  | 197 | 127
Assets, Fair Value Disclosure |  | 3,392 | 3,101
Fuel derivatives: |  |  |
Interest rate derivatives (see Note 10) |  | 0 | 0
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) |  |  |
Assets |  |  |
Treasury bills |  | 0 | 0
Interest rate derivatives (see Note 10) |  | 2 |
Fuel derivatives: |  |  |
Other available for sale securities |  | 0 | 0
Assets, Fair Value Disclosure |  | 879 | 715
Fuel derivatives: |  |  |
Interest rate derivatives (see Note 10) |  | (6) | (14)
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) |  |  |
Assets |  |  |
Treasury bills |  | 0 | 0
Interest rate derivatives (see Note 10) |  | 0 |
Fuel derivatives: |  |  |
Assets, Fair Value Disclosure |  | 110 | 138
Fuel derivatives: |  |  |
Interest rate derivatives (see Note 10) |  | 0 | 0
Cash Equivalents | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) |  |  |
Assets |  |  |
Cash equivalents | [1] | 1,999 | 1,392
Cash Equivalents | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) |  |  |
Assets |  |  |
Cash equivalents | [1] | 0 | 0
Cash Equivalents | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) |  |  |
Assets |  |  |
Cash equivalents | [1] | 0 | 0
Commercial paper | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) |  |  |
Assets |  |  |
Cash equivalents |  | 0 | 0
Commercial paper | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) |  |  |
Assets |  |  |
Cash equivalents |  | 535 | 454
Commercial paper | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) |  |  |
Assets |  |  |
Cash equivalents |  | 0 | 0
Certificates of deposit | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) |  |  |
Assets |  |  |
Cash equivalents |  | 0 | 0
Certificates of deposit | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) |  |  |
Assets |  |  |
Cash equivalents |  | 14 | 8
Certificates of deposit | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) |  |  |
Assets |  |  |
Cash equivalents |  | 0 | 0
Certificates of deposit | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) |  |  |
Assets |  |  |
Investments |  | 0 | 0
Certificates of deposit | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) |  |  |
Assets |  |  |
Investments |  | 268 | 228
Certificates of deposit | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) |  |  |
Assets |  |  |
Investments |  | 0 | 0
Bank Time Deposits [Member] | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) |  |  |
Assets |  |  |
Investments |  | 0 |
Bank Time Deposits [Member] | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) |  |  |
Assets |  |  |
Investments |  | 25 |
Bank Time Deposits [Member] | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) |  |  |
Assets |  |  |
Investments |  | 0 |
Options Held | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) |  |  |
Fuel derivatives: |  |  |
Derivative Asset, Fair Value, Gross Asset | [2] | 0 | 0
Options Held | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) |  |  |
Fuel derivatives: |  |  |
Derivative Asset, Fair Value, Gross Asset | [2] | 0 | 0
Options Held | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) |  |  |
Fuel derivatives: |  |  |
Derivative Asset, Fair Value, Gross Asset | [2] | 110 | 138
Period end date | Fair Value, Measurements, Recurring |  |  |
Assets |  |  |
Treasury bills |  | 1,196 | 1,582
Interest rate derivatives (see Note 10) |  | 2 |
Fuel derivatives: |  |  |
Other available for sale securities |  | 197 | 127
Assets, Fair Value Disclosure |  | 4,381 | 3,954
Fuel derivatives: |  |  |
Interest rate derivatives (see Note 10) |  | (6) | (14)
Period end date | Cash Equivalents | Fair Value, Measurements, Recurring |  |  |
Assets |  |  |
Cash equivalents | [1] | 1,999 | 1,392
Period end date | Commercial paper | Fair Value, Measurements, Recurring |  |  |
Assets |  |  |
Cash equivalents |  | 535 | 454
Period end date | Certificates of deposit | Fair Value, Measurements, Recurring |  |  |
Assets |  |  |
Cash equivalents |  | 14 | 8
Period end date | Certificates of deposit | Fair Value, Measurements, Recurring |  |  |
Assets |  |  |
Investments |  | 268 | 228
Period end date | Bank Time Deposits [Member] | Fair Value, Measurements, Recurring |  |  |
Assets |  |  |
Investments |  | 25 |
Period end date | Options Held | Fair Value, Measurements, Recurring |  |  |
Fuel derivatives: |  |  |
Derivative Asset, Fair Value, Gross Asset | [2] | $ 110 | $ 138
[1] | Cash equivalents are primarily composed of money market investments.
[2] | In the Consolidated Balance Sheet amounts are presented as an asset. See Note 10.

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