Commitments and Contingencies - Aircraft Purchase and Lease Commitments (Details) $ in Millions	Sep. 30, 2015 USD ($) aircraft
Future aircraft purchase commitments
Unrecorded Unconditional Purchase Obligation [Line Items]
Future aircraft purchase commitments | $	$ 12,970
B-717-200 | Future aircraft purchase commitments
Unrecorded Unconditional Purchase Obligation [Line Items]
Aircraft purchase commitments, minimum quantity required	3
B-717-200 | Southwest Airlines and The Boeing Company
Unrecorded Unconditional Purchase Obligation [Line Items]
Other aircraft commitments	8
B-737-900ER | Future aircraft purchase commitments
Unrecorded Unconditional Purchase Obligation [Line Items]
Aircraft purchase commitments, minimum quantity required	54
A321-200 | Future aircraft purchase commitments
Unrecorded Unconditional Purchase Obligation [Line Items]
Aircraft purchase commitments, minimum quantity required	45
A330-900 NEO | Future aircraft purchase commitments
Unrecorded Unconditional Purchase Obligation [Line Items]
Aircraft purchase commitments, minimum quantity required	25
A350-900 | Future aircraft purchase commitments
Unrecorded Unconditional Purchase Obligation [Line Items]
Aircraft purchase commitments, minimum quantity required	25
B-787-8 | Future aircraft purchase commitments
Unrecorded Unconditional Purchase Obligation [Line Items]
Aircraft purchase commitments, minimum quantity required	18
A330-300 | Future aircraft purchase commitments
Unrecorded Unconditional Purchase Obligation [Line Items]
Aircraft purchase commitments, minimum quantity required	7
B-757-200 | Future aircraft purchase commitments
Unrecorded Unconditional Purchase Obligation [Line Items]
Aircraft purchase commitments, minimum quantity required	1