Income Taxes - Income Tax Provision (Benefit) Differed from Amounts Computed at the Statutory Federal Income Tax Rate and Significant Components (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Income Taxes [Line Items]
Income tax provision at statutory rate	$ 822	$ 556		$ 1,058
State income taxes, net of federal income tax benefit	50	29		30
Foreign tax rate differential	(90)	(84)		(43)
Global intangible low-taxed income	90	4		0
Foreign income taxes	1	2		3
Nondeductible employee meals	12	12		17
Impact of Tax Act	0	(5)		(189)
State rate change	0	3		12
Valuation allowance	(4)	(3)		(16)
Other, net	24	12		8
Income tax expense (benefit)	905	526	[1]	880	[1]
Current	23	14		(77)
Deferred	882	512	[2]	957	[2]
Valuation allowance recorded	58	59
United Airlines, Inc.
Income Taxes [Line Items]
Income tax provision at statutory rate	822	557		1,059
State income taxes, net of federal income tax benefit	50	29		30
Foreign tax rate differential	(90)	(84)		(43)
Global intangible low-taxed income	90	4		0
Foreign income taxes	1	2		3
Nondeductible employee meals	12	12		17
Impact of Tax Act	0	(5)		(206)
State rate change	0	3		12
Valuation allowance	(4)	(3)		(16)
Other, net	24	12		8
Income tax expense (benefit)	905	527	[3]	864	[3]
Current	23	14		(77)
Deferred	882	513	[4]	$ 941	[4]
Valuation allowance recorded	$ 58	$ 59

[1] Amounts adjusted due to the adoption of Accounting Standards Update No. 2016-02, Leases (Topic 842). 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. 2016-02, Leases (Topic 842). 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. 2016-02, Leases (Topic 842). 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. 2016-02, Leases (Topic 842). See Note 1 to the financial statements contained in Part II, Item 8 of this report for additional information.