Statements of Consolidated Stockholders' Equity - USD ($) $ in Millions		Total		Common Stock		Additional Capital Invested		Treasury Stock		Retained Earnings		Accumulated Other Comprehensive Income (Loss)		United Airlines, Inc.		United Airlines, Inc. Additional Capital Invested		United Airlines, Inc. Retained Earnings		United Airlines, Inc. Accumulated Other Comprehensive Income (Loss)		United Airlines, Inc. Receivable from Related Parties, Net
Balance (in shares) at Dec. 31, 2017	[1]			287,000,000.0
Balance at Dec. 31, 2017		$ 8,788	[1]	$ 3	[1]	$ 6,098	[1]	$ (769)	[1]	$ 4,603	[1]	$ (1,147)	[1]	$ 8,751	[2]	$ 1,787	[2]	$ 8,201	[2]	$ (1,147)	[2]	$ (90)	[2]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		1,661	[1],[3],[4]							1,661	[1]			1,662	[2],[5],[6]			1,662	[2]
Other comprehensive income (loss)		51	[3]									51		51	[6]					51
Dividend to UAL														(1,010)		(1,010)
Stock settled share-based compensation		45				45								45		45
Repurchases of common stock (in shares)				(14,700,000)
Repurchases of common stock		(1,010)						(1,010)
Net treasury stock issued for share-based awards (in shares)				200,000
Net treasury stock issued for share-based awards		(17)				(38)		26		(5)
Other														(19)				(7)		7		(19)
Balance (in shares) at Sep. 30, 2018	[1]			272,500,000
Balance at Sep. 30, 2018		9,518	[1]	$ 3	[1]	6,105	[1]	(1,753)	[1]	6,252	[1]	(1,089)	[1]	9,480	[2]	822	[2]	9,856	[2]	(1,089)	[2]	(109)	[2]
Balance (in shares) at Jun. 30, 2018	[1]			273,000,000.0
Balance at Jun. 30, 2018		8,691	[1]	$ 3	[1]	6,091	[1]	(1,720)	[1]	5,419	[1]	(1,102)	[1]	8,653	[2]	841	[2]	9,022	[2]	(1,102)	[2]	(108)	[2]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		833	[1],[3],[4]							833	[1]			834	[5],[6]			834
Other comprehensive income (loss)		13	[3]									13		13	[6]					13
Dividend to UAL														(34)		(34)
Stock settled share-based compensation		16				16								16		16
Repurchases of common stock (in shares)				(500,000)
Repurchases of common stock		(34)						(34)
Net treasury stock issued for share-based awards		(1)				(2)		1
Other														(2)		(1)						(1)
Balance (in shares) at Sep. 30, 2018	[1]			272,500,000
Balance at Sep. 30, 2018		$ 9,518	[1]	$ 3	[1]	6,105	[1]	(1,753)	[1]	6,252	[1]	(1,089)	[1]	$ 9,480	[2]	822	[2]	9,856	[2]	(1,089)	[2]	(109)	[2]
Balance (in shares) at Dec. 31, 2018		269,914,769		269,900,000	[1]									1,000
Balance at Dec. 31, 2018		$ 10,042	[1],[7]	$ 3	[1]	6,120	[1]	(1,993)	[1]	6,715	[1]	(803)	[1]	$ 10,004	[2],[8]	598	[2]	10,319	[2]	(803)	[2]	(110)	[2]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		2,368								2,368				2,369				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)								(32)
Balance (in shares) at Sep. 30, 2019		253,624,406		253,600,000										1,000
Balance at Sep. 30, 2019		$ 11,301		$ 3		6,111		(3,384)		9,075		(504)		$ 11,263		0		11,909		(504)		(142)
Balance (in shares) at Jun. 30, 2019				257,700,000
Balance at Jun. 30, 2019		10,320		$ 3		6,096		(3,022)		8,050		(807)		10,282		0		11,230		(807)		(141)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		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		$ (1)				(3)		1		1
Other														$ (1)								(1)
Balance (in shares) at Sep. 30, 2019		253,624,406		253,600,000										1,000
Balance at Sep. 30, 2019		$ 11,301		$ 3		$ 6,111		$ (3,384)		$ 9,075		$ (504)		$ 11,263		$ 0		$ 11,909		$ (504)		$ (142)

[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 I, Item 1 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 I, Item 1 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 I, Item 1 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 I, Item 1 of this report for additional information.

[5] 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 I, Item 1 of this report for additional information.

[6] 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 I, Item 1 of this report for additional information.

[7] 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 I, Item 1 of this report for additional information.

[8] 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 I, Item 1 of this report for additional information.