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Fair Value Measurements - Measured on Recurring Basis (Details) - USD ($) $ in Millions | Mar. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Fuel derivatives: |  |  |  |  |
Derivative Asset, Fair Value, Gross Asset | [1] | $ 345 |  | $ 444 |
Fuel derivatives: |  |  |  |  |
Derivative Liability, Fair Value, Gross Liability | [1] | (712) |  | (805) |
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) |  |  |  |  |
Assets |  |  |  |  |
Treasury bills |  | 1,347 |  | 1,345 |
Fuel derivatives: |  |  |  |  |
Other available for sale securities |  | 82 |  | 83 |
Total assets |  | 3,043 |  | 2,772 |
Liabilities |  |  |  |  |
Interest rate derivatives (see Note 3) |  | 0 |  | 0 |
Total Liabilities |  | 0 |  | 0 |
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) |  |  |  |  |
Assets |  |  |  |  |
Treasury bills |  | 0 |  | 0 |
Fuel derivatives: |  |  |  |  |
Other available for sale securities |  | 0 |  | 0 |
Total assets |  | 565 |  | 658 |
Liabilities |  |  |  |  |
Interest rate derivatives (see Note 3) |  | (30) |  | (35) |
Total Liabilities |  | (107) |  | (145) |
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) |  |  |  |  |
Assets |  |  |  |  |
Treasury bills |  | 0 |  | 0 |
Fuel derivatives: |  |  |  |  |
Other available for sale securities |  | 0 |  |  |
Total assets |  | 301 |  | 402 |
Liabilities |  |  |  |  |
Interest rate derivatives (see Note 3) |  | 0 |  | 0 |
Total Liabilities |  | (605) |  | (660) |
Cash Equivalents | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) |  |  |  |  |
Assets |  |  |  |  |
Cash equivalents |  | 1,614 | [2] | 1,344 | [3]
Cash Equivalents | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) |  |  |  |  |
Assets |  |  |  |  |
Cash equivalents |  | 0 | [2] | 0 | [3]
Cash Equivalents | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) |  |  |  |  |
Assets |  |  |  |  |
Cash equivalents |  | 0 | [2] | 0 | [3]
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 |  | 230 |  | 325 |
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 |  | 7 |  | 11 |
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 |  | 284 |  | 280 |
Certificates of deposit | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) |  |  |  |  |
Assets |  |  |  |  |
Investments |  | 0 |  | 0 |
Swap | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) |  |  |  |  |
Fuel derivatives: |  |  |  |  |
Derivative Liability, Fair Value, Gross Asset |  | 0 | [4] | 0 | [5]
Fuel derivatives: |  |  |  |  |
Derivative Liability, Fair Value, Gross Liability |  | 0 | [4] | 0 | [5]
Swap | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) |  |  |  |  |
Fuel derivatives: |  |  |  |  |
Derivative Liability, Fair Value, Gross Asset |  | 44 | [4] | 42 | [5]
Fuel derivatives: |  |  |  |  |
Derivative Liability, Fair Value, Gross Liability |  | (77) | [4] | (110) | [5]
Swap | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) |  |  |  |  |
Fuel derivatives: |  |  |  |  |
Derivative Liability, Fair Value, Gross Asset |  | 0 | [4] | 0 | [5]
Fuel derivatives: |  |  |  |  |
Derivative Liability, Fair Value, Gross Liability |  | 0 | [4] | 0 | [5]
Options Held | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) |  |  |  |  |
Fuel derivatives: |  |  |  |  |
Derivative Asset, Fair Value, Gross Asset |  | 0 | [6] | 0 | [7]
Derivative Liability, Fair Value, Gross Asset |  | 0 | [4] | 0 | [5]
Fuel derivatives: |  |  |  |  |
Derivative Asset, Fair Value, Gross Liability |  | 0 | [6] | 0 | [7]
Derivative Liability, Fair Value, Gross Liability |  | 0 | [4] | 0 | [5]
Options Held | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) |  |  |  |  |
Fuel derivatives: |  |  |  |  |
Derivative Asset, Fair Value, Gross Asset |  | 0 | [6] | 0 | [7]
Derivative Liability, Fair Value, Gross Asset |  | 0 | [4] | 0 | [5]
Fuel derivatives: |  |  |  |  |
Derivative Asset, Fair Value, Gross Liability |  | 0 | [6] | 0 | [7]
Derivative Liability, Fair Value, Gross Liability |  | 0 | [4] | 0 | [5]
Options Held | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) |  |  |  |  |
Fuel derivatives: |  |  |  |  |
Derivative Asset, Fair Value, Gross Asset |  | 132 | [6] | 239 | [7]
Derivative Liability, Fair Value, Gross Asset |  | 169 | [4] | 163 | [5]
Fuel derivatives: |  |  |  |  |
Derivative Asset, Fair Value, Gross Liability |  | (46) | [6] | (96) | [7]
Derivative Liability, Fair Value, Gross Liability |  | (559) | [4] | (564) | [5]
Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring |  |  |  |  |
Assets |  |  |  |  |
Treasury bills |  | 1,347 |  | 1,345 |
Fuel derivatives: |  |  |  |  |
Other available for sale securities |  | 82 |  | 83 |
Total assets |  | 3,909 |  | 3,832 |
Liabilities |  |  |  |  |
Interest rate derivatives (see Note 3) |  | (30) |  | (35) |
Total Liabilities |  | (712) |  | (805) |
Estimate of Fair Value Measurement [Member] | Cash Equivalents | Fair Value, Measurements, Recurring |  |  |  |  |
Assets |  |  |  |  |
Cash equivalents |  | 1,614 | [2] | 1,344 | [3]
Estimate of Fair Value Measurement [Member] | Commercial paper | Fair Value, Measurements, Recurring |  |  |  |  |
Assets |  |  |  |  |
Cash equivalents |  | 230 |  | 325 |
Estimate of Fair Value Measurement [Member] | Certificates of deposit | Fair Value, Measurements, Recurring |  |  |  |  |
Assets |  |  |  |  |
Cash equivalents |  | 7 |  | 11 |
Estimate of Fair Value Measurement [Member] | Certificates of deposit | Fair Value, Measurements, Recurring |  |  |  |  |
Assets |  |  |  |  |
Investments |  | 284 |  | 280 |
Estimate of Fair Value Measurement [Member] | Swap | Fair Value, Measurements, Recurring |  |  |  |  |
Fuel derivatives: |  |  |  |  |
Derivative Liability, Fair Value, Gross Asset |  | 44 | [4] | 42 | [5]
Fuel derivatives: |  |  |  |  |
Derivative Liability, Fair Value, Gross Liability |  | (77) | [4] | (110) | [5]
Estimate of Fair Value Measurement [Member] | Options Held | Fair Value, Measurements, Recurring |  |  |  |  |
Fuel derivatives: |  |  |  |  |
Derivative Asset, Fair Value, Gross Asset |  | 132 | [6] | 239 | [7]
Derivative Liability, Fair Value, Gross Asset |  | 169 | [4] | 163 | [5]
Fuel derivatives: |  |  |  |  |
Derivative Asset, Fair Value, Gross Liability |  | (46) | [6] | (96) | [7]
Derivative Liability, Fair Value, Gross Liability |  | $ (559) | [4] | $ (564) | [5]
[1] | Represents the position of each trade before consideration of offsetting positions with each counterparty and does not include the impact of cash collateral deposits provided to or received from counterparties. See discussion of credit risk and collateral following in this Note.
[2] | Cash equivalents are primarily composed of money market investments.
[3] | Cash equivalents are primarily composed of money market investments.
[4] | In the unaudited Condensed Consolidated Balance Sheet amounts are presented as a net liability. See Note 3.
[5] | In the unaudited Consolidated Balance Sheet amounts are presented as a net liability. See Note 3.
[6] | In the unaudited Condensed Consolidated Balance Sheet amounts are presented as a net asset. See Note 3.
[7] | In the unaudited Consolidated Balance Sheet amounts are presented as a net asset. See Note 3.

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