Statements of Consolidated Stockholders' Equity (Unaudited) - USD ($) $ in Millions	Total		United Airlines, Inc.	Adoption of New Accounting Standard	[1]	Adoption of New Accounting Standard United Airlines, Inc.	[2]	Common Stock		Additional Capital Invested	Additional Capital Invested United Airlines, Inc.	Treasury Stock	Retained Earnings	Retained Earnings United Airlines, Inc.	Retained Earnings Adoption of New Accounting Standard	[1]	Retained Earnings Adoption of New Accounting Standard United Airlines, Inc.	[2]	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) United Airlines, Inc.	(Receivable from) Payable to Related Parties, Net United Airlines, Inc.
Balance (in shares) at Dec. 31, 2018								269,900,000
Balance at Dec. 31, 2018	$ 10,042		$ 10,004					$ 3		$ 6,120	$ 598	$ (1,993)	$ 6,715	$ 10,319					$ (803)	$ (803)	$ (110)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	2,368		2,369										2,368	2,369
Other comprehensive income (loss)	299		299																299	299
Dividend to UAL			(1,426)								(647)			(779)
Stock settled share-based compensation	49		49							49	49
Repurchases of common stock (in shares)								(16,800,000)
Repurchases of common stock	(1,426)											(1,426)
Net treasury stock issued for share-based awards (in shares)								500,000
Net treasury stock issued for share-based awards	(31)									(58)		35	(8)
Other			(32)											0						0	(32)
Balance (in shares) at Sep. 30, 2019								253,600,000
Balance at Sep. 30, 2019	11,301		11,263					$ 3		6,111	0	(3,384)	9,075	11,909					(504)	(504)	(142)
Balance (in shares) at Jun. 30, 2019								257,700,000
Balance at Jun. 30, 2019	10,320		10,282					$ 3		6,096	0	(3,022)	8,050	11,230					(807)	(807)	(141)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	1,024		1,024										1,024	1,024
Other comprehensive income (loss)	303		303																303	303
Dividend to UAL			(363)								(18)			(345)
Stock settled share-based compensation	18		18							18	18
Repurchases of common stock (in shares)								(4,100,000)
Repurchases of common stock	(363)											(363)
Net treasury stock issued for share-based awards (in shares)								0
Net treasury stock issued for share-based awards	(1)									(3)		1	1
Other			(1)								0										(1)
Balance (in shares) at Sep. 30, 2019								253,600,000
Balance at Sep. 30, 2019	$ 11,301		$ 11,263					$ 3		6,111	0	(3,384)	9,075	11,909					(504)	(504)	(142)
Balance (in shares) at Dec. 31, 2019	251,216,381		1,000					251,200,000	[1]
Balance at Dec. 31, 2019	$ 11,531	[1]	$ 11,492	$ (17)		$ (17)		$ 3		6,129	0	(3,599)	9,716	12,353	$ (17)		$ (17)		(718)	(718)	(143)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(5,172)		(5,171)										(5,172)	(5,171)
Other comprehensive income (loss)	(291)		(291)																(291)	(291)
Dividend to UAL			(342)								(12)			(330)
Stock settled share-based compensation	80		80							80	80
Sale of common stock (in shares)								43,700,000
Sale of common stock	1,135									1,135
Repurchases of common stock (in shares)								(4,400,000)
Repurchases of common stock	(342)											(342)
Warrants issued	97									97
Net treasury stock issued for share-based awards (in shares)								500,000
Net treasury stock issued for share-based awards	$ (18)									(58)		43	(3)
Other			$ 1,221																		1,221
Balance (in shares) at Sep. 30, 2020	290,990,454		1,000					291,000,000.0
Balance at Sep. 30, 2020	$ 7,003		$ 6,972					$ 3		7,383	68	(3,898)	4,524	6,835					(1,009)	(1,009)	1,078
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member		us-gaap:AccountingStandardsUpdate201613Member
Balance (in shares) at Jun. 30, 2020								291,000,000.0
Balance at Jun. 30, 2020	$ 8,517		$ 8,485					$ 3		7,307	30	(3,899)	6,365	8,676					(1,259)	(1,259)	1,038
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(1,841)		(1,841)										(1,841)	(1,841)
Other comprehensive income (loss)	250		250																250	250
Stock settled share-based compensation	38		38							38	38
Warrants issued	40									40
Net treasury stock issued for share-based awards (in shares)								0
Net treasury stock issued for share-based awards	$ (1)									(2)		1	0
Other			$ 40																		40
Balance (in shares) at Sep. 30, 2020	290,990,454		1,000					291,000,000.0
Balance at Sep. 30, 2020	$ 7,003		$ 6,972					$ 3		$ 7,383	$ 68	$ (3,898)	$ 4,524	$ 6,835					$ (1,009)	$ (1,009)	$ 1,078

[1] Transition adjustment due to the adoption of Accounting Standards Update No. 2016-13, Financial Instruments—Credit Losses. See Note 1 to the financial statements contained in Part I, Item 1 of this report for additional information.

[2] Transition adjustment due to the adoption of Accounting Standards Update No. 2016-13, Financial Instruments—Credit Losses. See Note 1 to the financial statements contained in Part I, Item 1 of this report for additional information.