Leases and Capacity Purchase Agreements - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) Aircraft	Dec. 31, 2015 USD ($) Aircraft	Dec. 31, 2014 USD ($)
Capital Leased Assets [Line Items]
Regional capacity purchase expense | $		$ 2,197	$ 2,290	$ 2,344
Capacity Purchase Agreements | Scenario Forecast
Capital Leased Assets [Line Items]
Scheduled block hours increase (decrease) percentage	10.00%
Change in cash obligation | $	$ 147
Metropolitan Washington Airports Authority
Capital Leased Assets [Line Items]
Operating lease expiration date, in years		2024
Lease extension term		7 years
Aircraft Operating Leases
Capital Leased Assets [Line Items]
Operating leases obligations | $		$ 6,508
Facility and Other Operating Leases
Capital Leased Assets [Line Items]
Operating lease extended expiration year		2041
Operating leases obligations | $		$ 12,047
Minimum | Aircraft Operating Leases
Capital Leased Assets [Line Items]
Operating lease term		5 years
Operating lease expiration date, in years		2017
Maximum | Aircraft Operating Leases
Capital Leased Assets [Line Items]
Operating lease term		26 years
Operating lease expiration date, in years		2028
United Airlines, Inc.
Capital Leased Assets [Line Items]
Nonaircraft rent expense | $		$ 1,200	1,300	1,400
Regional capacity purchase expense | $		$ 2,197	2,290	2,344
United Airlines, Inc. | Capacity Purchase Agreements
Capital Leased Assets [Line Items]
Number of aircraft operated		494
Airline capacity purchase arrangements, expiration year		2029
United Airlines, Inc. | Revaluation of Liabilities
Capital Leased Assets [Line Items]
Net accretion amounts | $		$ 82	107	160
United Airlines, Inc. | Regional Aircraft
Capital Leased Assets [Line Items]
Regional capacity purchase expense | $		439	$ 461	$ 442
United Airlines, Inc. | Variable Interest Entity, Not Primary Beneficiary
Capital Leased Assets [Line Items]
Operating leases obligations | $		$ 1,400
United Airlines, Inc. | Minimum
Capital Leased Assets [Line Items]
Imputed interest rate		3.50%
Lease Fair Value Adjustment, Remaining Lease Term		1 year
United Airlines, Inc. | Maximum
Capital Leased Assets [Line Items]
Imputed interest rate		20.80%
Lease Fair Value Adjustment, Remaining Lease Term		8 years
United Airlines, Inc. | Mainline
Capital Leased Assets [Line Items]
Number of assets subject to lease		38
United Airlines, Inc. | Regional Carrier
Capital Leased Assets [Line Items]
Number of assets subject to lease		29
AerCap Holdings N.V. | A319 aircraft | Capital Addition Purchase Commitments
Capital Leased Assets [Line Items]
Number of aircraft expected to be delivered		5
AerCap Holdings N.V. | Maximum | A319 aircraft | Capital Addition Purchase Commitments
Capital Leased Assets [Line Items]
Number of used aircraft expected to be delivered over the next five years			14
SkyWest | Embraer E175 Aircraft | Capital Addition Purchase Commitments | Capacity Purchase Arrangement
Capital Leased Assets [Line Items]
Number of aircraft expected to be delivered		7
Number of aircraft operated			25
Mesa | Embraer E175 Aircraft | Capital Addition Purchase Commitments | Capacity Purchase Arrangement
Capital Leased Assets [Line Items]
Number of aircraft committed to purchase		12
Number of aircraft to be acquired		12
CommutAir | Embraer ERJ145 Aircraft | Capacity Purchase Arrangement
Capital Leased Assets [Line Items]
Number of aircraft operated			40
Used aircraft, scheduled transfer end date			2018
Number of aircrafts to be transferred		28
Republic | Embraer E175 Aircraft | Capital Addition Purchase Commitments | Capacity Purchase Arrangement
Capital Leased Assets [Line Items]
Number of aircraft expected to be delivered		12
Number of aircraft operated		28	28
Number of aircraft Purchased		16
Number of aircraft delivered		16
Number of aircraft owned		12