Schedule of Commitments to Purchase Aircrafts (Detail) - United Airlines, Inc. - Capital Addition Purchase Commitments	Sep. 30, 2017 Aircraft	[1]
Airbus A350 Aircraft
Long-term Purchase Commitment [Line Items]
Number of new aircraft committed to purchase	45
Boeing 737 MAX Aircraft
Long-term Purchase Commitment [Line Items]
Number of new aircraft committed to purchase	161
Boeing 777-300ER Aircraft
Long-term Purchase Commitment [Line Items]
Number of new aircraft committed to purchase	4
Boeing 787 Aircraft
Long-term Purchase Commitment [Line Items]
Number of new aircraft committed to purchase	18
Embraer E175 Aircraft
Long-term Purchase Commitment [Line Items]
Number of new aircraft committed to purchase	5

[1] United also has options and purchase rights for additional aircraft.