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Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2018 | Mar. 31, 2017
Reclassification Out of Accumulated Other Comprehensive Income [Line Items] |  |
Fuel and oil | $ 1,018 | $ 956
Interest Expense | (32) | (29)
Less: Tax Expense | (139) | $ (193)
Reclassification out of Accumulated Other Comprehensive Income |  |
Reclassification Out of Accumulated Other Comprehensive Income [Line Items] |  |
Net of Tax | 5 |
Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income |  |
Reclassification Out of Accumulated Other Comprehensive Income [Line Items] |  |
Less: Tax Expense | 1 |
Net of Tax | 3 |
Interest rate derivatives | Reclassification out of Accumulated Other Comprehensive Income |  |
Reclassification Out of Accumulated Other Comprehensive Income [Line Items] |  |
Less: Tax Expense | 0 |
Net of Tax | 2 |
Fuel derivatives |  |
Reclassification Out of Accumulated Other Comprehensive Income [Line Items] |  |
Reclassification to earnings | 4 |
Interest rate derivatives |  |
Reclassification Out of Accumulated Other Comprehensive Income [Line Items] |  |
Reclassification to earnings | $ 2 |

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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 tax of reclassification adjustments of other comprehensive income (loss). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 55 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=84158357&loc=d3e1436-108581 + Details
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