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Accumulated Other Comprehensive Income (Loss) - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |
Interest Expense | $ 114 | $ 122 | $ 121
Fuel and oil | 3,940 | 3,647 | 3,616
Less: Tax Expense | (237) | $ 1,303 | $ 1,298
Reclassification out of Accumulated Other Comprehensive Income |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |
Net of tax | 356 |  |
Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |
Fuel and oil | 552 |  |
Less: Tax Expense | 203 |  |
Net of tax | 349 |  |
Interest rate derivatives | Reclassification out of Accumulated Other Comprehensive Income |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |
Interest Expense | 11 |  |
Less: Tax Expense | 4 |  |
Net of tax | $ 7 |  |

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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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- Definition Amount of the cost of borrowed funds accounted for as interest expense. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.9) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 + Details
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- Definition Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=96947427&loc=d3e1377-109256 + Details
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