Commitments and Contingencies - Aircraft-Related Commitments and Financing Arrangements (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014 aircraft
Airbus
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of aircraft with secured debt financing commitments scheduled for delivery	6
Number of aircraft without secured financing commitments scheduled for delivery	95
Number of aircraft with signed letters of intent, scheduled for delivery	5
Third-Party Lessor
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of direct leased aircraft ordered from a third party	5
Aircraft and Related Flight Equipment
Unrecorded Unconditional Purchase Obligation [Line Items]
Committed expenditures, 2015	660.1
Committed expenditures, 2016	604.0
Committed expenditures, 2017	763.4
Committed expenditures, 2018	621.4
Committed expenditures, 2019	711.1
Committed expenditures, 2020 and beyond	1,525.3
Reservation System and Advertising Media
Unrecorded Unconditional Purchase Obligation [Line Items]
Committed expenditures, 2015	5.1
Committed expenditures, 2016	3.9
Committed expenditures, 2017	3.9
Committed expenditures, 2018	2.6
Committed expenditures, 2019	0
Committed expenditures, 2020 and beyond	0
V2500 SelectOne Engine
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of spare aircraft engines ordered	5
PurePower PW1100G-JM Engine
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of spare aircraft engines ordered	9

Number of Aircraft without Secured Financing Commitments Scheduled for Delivery

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Number of Aircraft with Secured Debt Financing Commitments Scheduled for Delivery

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Number of Aircraft with Signed Letters of Intent, Scheduled for Delivery

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Number of Direct Leased Aircraft Ordered From A Third Party

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Number of Spare Aircraft Engines Ordered

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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.

+ References

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=6394976&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.

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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.

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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 fixed and determinable portion of the unrecorded unconditional purchase obligation maturing in the third 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 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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