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Differences between Net Income and Comprehensive Income (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2018 | Mar. 31, 2017
Condensed Statement of Income Captions [Line Items] |  |
Net income | $ 463 | $ 339
Other Comprehensive Income (Loss), Net of Tax | 84 | 11
Comprehensive Income (Loss), Net of Tax, Attributable to Parent | 547 | 350
Fuel derivatives |  |
Condensed Statement of Income Captions [Line Items] |  |
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax | 81 | 9
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax | 25 | 5
Interest rate derivatives |  |
Condensed Statement of Income Captions [Line Items] |  |
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax | 3 | 2
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax | $ 0 | $ 1
Reclassification out of Accumulated Other Comprehensive Income |  |
Condensed Statement of Income Captions [Line Items] |  |
Reclassification of Stranded amounts in AOCI to Retained Earnings (ASU 2018-02) | 2 |

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- Definition Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e557-108580 + Details
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