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Financial Derivative Instruments - (Gain) Loss by Hedging Relationship (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
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Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018
Cash Flow Hedging |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
(Gain) loss recognized in AOCI on derivatives | $ 70 | $ (229) | $ 15 | $ (308)
Fuel derivatives | Cash Flow Hedging |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
(Gain) loss recognized in AOCI on derivatives | 54 | (228) | (12) | (306)
Interest rate derivatives | Cash Flow Hedging |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
(Gain) loss recognized in AOCI on derivatives | 16 | (1) | 27 | (2)
Interest rate derivatives | Interest rate derivatives | Not Designated as Hedging Instrument |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Gain recognized in income on derivatives | $ 0 | $ (1) | $ 0 | $ (2)

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- Definition Amount of increase (decrease) in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959 + Details
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- Definition Amount before tax of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=114867106&loc=d3e637-108580 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=109978405&loc=d3e80720-113993 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669646-108580 + Details
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