Statements of Consolidated Stockholders' Equity (Unaudited) - USD ($) $ in Millions	Total		United Airlines, Inc.		Adoption of New Accounting Standard	[2]	Adoption of New Accounting Standard United Airlines, Inc.	[1]	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	[2]	Retained Earnings Adoption of New Accounting Standard United Airlines, Inc.	[1]	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) United Airlines, Inc.	Receivable from 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)	1,344		1,345	[1]										1,344	1,345	[1]
Other comprehensive income (loss)	(4)		(4)																		(4)	(4)
Dividend to UAL			(1,063)									(629)			(434)
Stock settled share-based compensation	31		31								31	31
Repurchases of common stock (in shares)									(12,700,000)
Repurchases of common stock	(1,063)												(1,063)
Net treasury stock issued for share-based awards (in shares)									500,000
Net treasury stock issued for share-based awards	(30)										(55)		34	(9)
Other			(31)												0							0	(31)
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)
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)
Balance (in shares) at Dec. 31, 2019	251,216,381		1,000						251,200,000	[2]
Balance at Dec. 31, 2019	$ 11,531	[2]	$ 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]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member		us-gaap:AccountingStandardsUpdate201613Member
Balance (in shares) at Mar. 31, 2019									264,300,000
Balance at Mar. 31, 2019	$ 9,802		$ 9,763						$ 3		6,080	84	(2,487)	6,999	10,612						(793)	(793)	(140)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	1,052		1,052											1,052	1,052
Other comprehensive income (loss)	(14)		(14)																		(14)	(14)
Dividend to UAL			(536)									(102)			(434)
Stock settled share-based compensation	17		17								17	17
Repurchases of common stock (in shares)									(6,600,000)
Repurchases of common stock	(536)												(536)
Net treasury stock issued for share-based awards (in shares)									0
Net treasury stock issued for share-based awards	(1)										(1)		1	(1)
Other			0									1											(1)
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)
Balance (in shares) at Dec. 31, 2019	251,216,381		1,000						251,200,000	[2]
Balance at Dec. 31, 2019	$ 11,531	[2]	$ 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)	(3,331)		(3,330)											(3,331)	(3,330)
Other comprehensive income (loss)	(541)		(541)																		(541)	(541)
Dividend to UAL			(342)									(12)			(330)
Stock settled share-based compensation	42		42								42	42
Repurchases of common stock (in shares)									(4,400,000)
Repurchases of common stock	(342)												(342)
Sale of common stock (in shares)									43,700,000
Sale of common stock	1,135										1,135
Warrants issued	57										57
Net treasury stock issued for share-based awards (in shares)									500,000
Net treasury stock issued for share-based awards	$ (17)										(56)		42	(3)
Other			$ 1,181																				1,181
Balance (in shares) at Jun. 30, 2020	290,982,216		1,000						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]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Balance (in shares) at Mar. 31, 2020									247,300,000
Balance at Mar. 31, 2020	$ 9,418		9,380						$ 3		6,096	10	(3,901)	7,991	10,302						(771)	(771)	(161)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(1,627)		(1,626)											(1,627)	(1,626)
Other comprehensive income (loss)	(488)		(488)																		(488)	(488)
Stock settled share-based compensation	20		20								20	20
Sale of common stock (in shares)									43,700,000
Sale of common stock	1,135										1,135
Warrants issued	57										57
Net treasury stock issued for share-based awards (in shares)									0
Net treasury stock issued for share-based awards	$ 2										(1)		2	1
Other			$ 1,199																				1,199
Balance (in shares) at Jun. 30, 2020	290,982,216		1,000						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

[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.