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Comprehensive Income (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016
Accumulated Other Comprehensive Income Loss [Line Items] |  |  |  |
Net income | $ 503 | $ 388 | $ 1,600 | $ 1,722
Other, net of deferred taxes | 2 | 3 | 4 | 3
Total other comprehensive income (loss) | 127 | 129 | 187 | 552
Total comprehensive income | 630 | 517 | 1,787 | 2,274
Deferred taxes on unrealized gain (loss) on other | 2 | 2 | 2 | 2
Less: Tax Expense | 288 | 230 | 913 | 1,016
Interest Expense | (28) | (31) | (84) | (93)
Fuel derivatives |  |  |  |
Accumulated Other Comprehensive Income Loss [Line Items] |  |  |  |
Beginning Balance | (412) |  | (499) |
Changes in fair value | 45 |  | (165) |
Reclassification to earnings | 151 |  | 448 |
Ending Balance | (216) |  | (216) |
Interest rate derivatives |  |  |  |
Accumulated Other Comprehensive Income Loss [Line Items] |  |  |  |
Beginning Balance | (13) |  | (18) |
Changes in fair value | 0 |  | (1) |
Reclassification to earnings | 2 |  | 8 |
Ending Balance | (11) |  | (11) |
Defined benefit plan items |  |  |  |
Accumulated Other Comprehensive Income Loss [Line Items] |  |  |  |
Beginning Balance | (14) |  | (14) |
Changes in fair value | 0 |  | 0 |
Reclassification to earnings | 0 |  | 0 |
Ending Balance | (14) |  | (14) |
Other |  |  |  |
Accumulated Other Comprehensive Income Loss [Line Items] |  |  |  |
Beginning Balance | 22 |  | 20 |
Changes in fair value | 4 |  | 6 |
Reclassification to earnings | 0 |  | 0 |
Ending Balance | 26 |  | 26 |
Deferred Tax |  |  |  |
Accumulated Other Comprehensive Income Loss [Line Items] |  |  |  |
Beginning Balance | 154 |  | 188 |
Changes in fair value | (18) |  | 59 |
Reclassification to earnings | (57) |  | (168) |
Ending Balance | 79 |  | 79 |
AOCI Including Portion Attributable to Noncontrolling Interest |  |  |  |
Accumulated Other Comprehensive Income Loss [Line Items] |  |  |  |
Beginning Balance | (263) |  | (323) |
Changes in fair value | 31 |  | (101) |
Reclassification to earnings | 96 |  | 288 |
Ending Balance | (136) |  | (136) |
Interest rate derivatives |  |  |  |
Accumulated Other Comprehensive Income Loss [Line Items] |  |  |  |
Unrealized gain (loss) on derivatives, net of tax | 2 | 4 | 5 | 3
Deferred taxes on unrealized gain (loss) on derivatives | 0 | 2 | 2 | 1
Fuel derivatives |  |  |  |
Accumulated Other Comprehensive Income Loss [Line Items] |  |  |  |
Unrealized gain (loss) on derivatives, net of tax | 123 | 122 | 178 | 546
Deferred taxes on unrealized gain (loss) on derivatives | $ 73 | $ 72 | $ 105 | $ 321

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