Commitments and Contingencies - Commitments (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Aircraft and Related Flight Equipment [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation, Due in Remainder of Fiscal Year	$ 412.0
Unrecorded Unconditional Purchase Obligation, Due within Two Years	662.0
Unrecorded Unconditional Purchase Obligation, Due within Three Years	601.0
Unrecorded Unconditional Purchase Obligation, Due within Four Years	757.0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	616.0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	2,211.0
Reservation System Provider and Advertising Media [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation, Due in Remainder of Fiscal Year	3.2
Unrecorded Unconditional Purchase Obligation, Due within Two Years	3.9
Unrecorded Unconditional Purchase Obligation, Due within Three Years	3.9
Unrecorded Unconditional Purchase Obligation, Due within Four Years	3.9
Unrecorded Unconditional Purchase Obligation, Due within Five Years	2.6
Unrecorded Unconditional Purchase Obligation, Due after Five Years	$ 0
V2500 SelectOne Engine [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of spare aircraft engines ordered (in aircraft engine)	6
PurePower PW1100G-JM Engine [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of spare aircraft engines ordered (in aircraft engine)	9
Airbus [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of Aircraft with Secured Financing Commitments Scheduled for Delivery (in aircraft)	5
Number of Aircraft without Secured Financing Commitments Scheduled for Delivery (in aircraft)	105