Commitments and Contingencies - Aircraft Purchase Commitments and Contract Carrier Agreements (Details) $ in Millions	Dec. 31, 2017 USD ($) aircraft
Future aircraft purchase commitments
Unrecorded Unconditional Purchase Obligation
2018	$ 3,570
2019	3,370
2020	3,270
2021	3,880
2022	2,450
Thereafter	1,740
Total	$ 18,280
Aircraft purchase commitments, minimum quantity required \| aircraft	353
Future aircraft purchase commitments \| A321-200
Unrecorded Unconditional Purchase Obligation
Aircraft purchase commitments, minimum quantity required \| aircraft	93
Future aircraft purchase commitments \| A321-200neo
Unrecorded Unconditional Purchase Obligation
Aircraft purchase commitments, minimum quantity required \| aircraft	100
Future aircraft purchase commitments \| A330-900neo
Unrecorded Unconditional Purchase Obligation
Aircraft purchase commitments, minimum quantity required \| aircraft	25
Future aircraft purchase commitments \| A350-900
Unrecorded Unconditional Purchase Obligation
Aircraft purchase commitments, minimum quantity required \| aircraft	19
Future aircraft purchase commitments \| B-737-900ER
Unrecorded Unconditional Purchase Obligation
Aircraft purchase commitments, minimum quantity required \| aircraft	41
Future aircraft purchase commitments \| CS100
Unrecorded Unconditional Purchase Obligation
Aircraft purchase commitments, minimum quantity required \| aircraft	75
Airline capacity purchase arrangements
Unrecorded Unconditional Purchase Obligation
2018	$ 1,772
2019	1,603
2020	1,320
2021	793
2022	723
Thereafter	1,975
Total	$ 8,186

Amount of the fixed and determinable portion of the unrecorded unconditional purchase obligation maturing in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 440
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=77896938&loc=d3e25336-109308

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Amount of the fixed and determinable portion of the unrecorded unconditional purchase obligation maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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Amount of the fixed and determinable portion of the unrecorded unconditional purchase obligation maturing in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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Amount of the fixed and determinable portion of the unrecorded unconditional purchase obligation maturing in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of the unrecorded obligation to transfer funds in the future for fixed or minimum amounts or quantities of goods or services at fixed or minimum prices (for example, as in take-or-pay contracts or throughput contracts).

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Amount of the fixed and determinable portion of the unrecorded unconditional purchase obligation maturing after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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The minimum number of units that must be purchased, in connection with an unconditional purchase obligation that has not been recognized for financial reporting purposes.

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