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Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Reclassification Out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |
Fuel and oil | $ 1,202 | $ 1,024 | $ 2,220 | $ 1,979
Interest Expense | (33) | (27) | (66) | (56)
Less: Tax Expense | (227) | $ (422) | (366) | $ (616)
Reclassification out of Accumulated Other Comprehensive Income |  |  |  |
Reclassification Out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |
Net of Tax | (12) |  | (7) |
Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income |  |  |  |
Reclassification Out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |
Reclassification to earnings | 16 |  | 12 |
Less: Tax Expense | (4) |  | (3) |
Net of Tax | (12) |  | (9) |
Interest rate derivatives | Reclassification out of Accumulated Other Comprehensive Income |  |  |  |
Reclassification Out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |
Less: Tax Expense | (1) |  | (1) |
Net of Tax | 0 |  | 2 |
Interest rate derivatives |  |  |  |
Reclassification Out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |
Reclassification to earnings | $ (1) |  | $ (3) |

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- Definition Fuel costs incurred that are directly related to goods produced and sold and services rendered during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2(a),(d)) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
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- Definition Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a),(b) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32639-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(h)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 + Details
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