Leases and Capacity Purchase Agreements - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) Aircraft	Dec. 31, 2017 USD ($)		Dec. 31, 2016 USD ($)		Dec. 31, 2015 USD ($)
Capital Leased Assets [Line Items]
Regional capacity purchase expense		$ 2,601	$ 2,232	[1]	$ 2,197	[1]
Expenses		38,011	34,113	[1]	32,214	[1]
Accounts payable		2,363	2,196	[2]
Capacity Purchase Agreements | Forecast
Capital Leased Assets [Line Items]
Scheduled block hours increase (decrease) percentage	10.00%
Change in cash obligation	$ 160
Aircraft Operating Leases
Capital Leased Assets [Line Items]
Operating leases obligations		$ 4,056
Minimum | Aircraft Operating Leases
Capital Leased Assets [Line Items]
Operating lease term		5 years
Operating lease expiration date		2019
Maximum | Aircraft Operating Leases
Capital Leased Assets [Line Items]
Operating lease term		26 years
Operating lease expiration date		2029
United Airlines, Inc.
Capital Leased Assets [Line Items]
Nonaircraft rent expense		$ 1,300	1,300		1,200
Regional capacity purchase expense		$ 2,601	2,232	[3]	2,197	[3]
Number of aircrafts under the extended term of contract | Aircraft		125
Capacity purchase agreement contract expiration date after extension		Dec. 31, 2022
Expenses		$ 38,009	34,111	[3]	32,212	[3]
Accounts payable		$ 2,363	2,196	[4]
United Airlines, Inc. | Capacity Purchase Agreements
Capital Leased Assets [Line Items]
Number of regional aircraft | Aircraft		559
Airline capacity purchase arrangements, expiration year		2029
United Airlines, Inc. | Revaluation of Liabilities
Capital Leased Assets [Line Items]
Net accretion amounts		$ 60	79				$ 82
United Airlines, Inc. | Variable Interest Entity, Not Primary Beneficiary
Capital Leased Assets [Line Items]
Operating leases obligations		1,300
United Airlines, Inc. | Regional Aircraft
Capital Leased Assets [Line Items]
Regional capacity purchase expense		$ 505	458		439
United Airlines, Inc. | Minimum
Capital Leased Assets [Line Items]
Imputed interest rate		3.50%
Remaining lease term		1 year
United Airlines, Inc. | Maximum
Capital Leased Assets [Line Items]
Imputed interest rate		115.10%
Remaining lease term		6 years
United Airlines, Inc. | Mainline
Capital Leased Assets [Line Items]
Number of assets subject to lease | Aircraft		28
United Airlines, Inc. | Regional Carrier
Capital Leased Assets [Line Items]
Number of assets subject to lease | Aircraft		90
United Airlines, Inc. | Regional Carrier | Capacity Purchase Agreements
Capital Leased Assets [Line Items]
Expenses		$ 979	907		$ 935
Accounts payable		53	24
Accounts receivable from regional carriers		$ 0	$ 0
CRJ 200 | United Airlines, Inc. | Maximum
Capital Leased Assets [Line Items]
Number of aircraft to operate | Aircraft		65
Chicago O'Hare | Airline Use and Lease Agreement - Chicago O'Hare
Capital Leased Assets [Line Items]
Operating lease term		15 years
Chicago O'Hare | Minimum | Hangars, Ground Equipment Maintenance Building and Employee Parking Lease
Capital Leased Assets [Line Items]
Operating lease term		15 years
Chicago O'Hare | Maximum | Hangars, Ground Equipment Maintenance Building and Employee Parking Lease
Capital Leased Assets [Line Items]
Operating lease term		30 years

[1] Amounts adjusted due to the adoption of Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606) and Accounting Standards Update No. 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. See Note 1 to the financial statements contained in Part II, Item 8 of this report for additional information.

[2] Amounts adjusted due to the adoption of Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606). See Note 1 to the financial statements contained in Part II, Item 8 of this report for additional information.

[3] Amounts adjusted due to the adoption of Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606) and Accounting Standards Update No. 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. See Note 1 to the financial statements contained in Part II, Item 8 of this report for additional information.

[4] Amounts adjusted due to the adoption of Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606). See Note 1 to the financial statements contained in Part II, Item 8 of this report for additional information.