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Accumulated Other Comprehensive Income - Schedule of AOCI Components (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017
Fuel derivatives |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest |  | $ 365 | $ 365 | $ 83 | $ 3
Changes in Fair Value |  | 298 | 400 |  |
ASU 2017-12 Adoption Adjustment | [1] |  | 26 |  |
Fuel derivatives | Accounting Standards Update 2018-02 |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |
Reclassification to earnings | [2] |  | 0 |  |
Interest rate derivatives |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest |  | (2) | (2) | (4) | (7)
Changes in Fair Value |  | 1 | 2 |  |
Reclassification to earnings |  | (1) | (3) |  |
ASU 2017-12 Adoption Adjustment | [1] |  | 0 |  |
Interest rate derivatives | Accounting Standards Update 2018-02 |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |
Reclassification to earnings | [2] |  | 0 |  |
Defined Benefit Plan Items |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest |  | (9) | (9) | (9) | (9)
Changes in Fair Value |  | 0 | 0 |  |
Reclassification to earnings |  | 0 | 0 |  |
ASU 2017-12 Adoption Adjustment | [1] |  | 0 |  |
Defined Benefit Plan Items | Accounting Standards Update 2018-02 |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |
Reclassification to earnings | [2] |  | 0 |  |
Other comprehensive income other changes net of tax |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest |  | 36 | 36 | 33 | 33
Changes in Fair Value |  | 3 | 3 |  |
Reclassification to earnings |  | 0 | 0 |  |
ASU 2017-12 Adoption Adjustment | [1] |  | 0 |  |
Other comprehensive income other changes net of tax | Accounting Standards Update 2018-02 |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |
Reclassification to earnings | [2] |  | 0 |  |
Deferred Tax |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest |  | (92) | (92) | (25) | (8)
Changes in Fair Value |  | (70) | (94) |  |
Reclassification to earnings |  | 3 | 2 |  |
ASU 2017-12 Adoption Adjustment | [1] |  | 6 |  |
Deferred Tax | Accounting Standards Update 2018-02 |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |
Reclassification to earnings | [2] |  | 2 |  |
AOCI Including Portion Attributable to Noncontrolling Interest |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest |  | 298 | 298 | $ 78 | $ 12
Changes in Fair Value |  | 232 | 311 |  |
Reclassification to earnings |  | $ (12) | (7) |  |
ASU 2017-12 Adoption Adjustment | [1] |  | (20) |  |
AOCI Including Portion Attributable to Noncontrolling Interest | Accounting Standards Update 2018-02 |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |
Reclassification to earnings | [2] |  | $ 2 |  |
[1] | The Company adopted the New Hedging Standard as of January 1, 2018. See Note 2 for further information on this adoption.
[2] | The Company adopted the Reclassification of Certain Tax Effects from AOCI as of January 1, 2018, which allowed the Company to reclassify to Retained earnings any tax effects stranded in AOCI as a result of the Tax Cuts and Jobs Act enacted in December 2017.

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