Statements of Consolidated Stockholder's Equity - USD ($) shares in Millions, $ in Millions	Total	United Airlines, Inc.	Common Stock	Additional Capital Invested	Additional Capital Invested United Airlines, Inc.	Treasury Stock	Accumulated Deficit	Accumulated Deficit United Airlines, Inc.	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) United Airlines, Inc.	Receivable from Related Parties, Net United Airlines, Inc.
Beginning Balance (in shares) at Dec. 31, 2014			375
Beginning Balance at Dec. 31, 2014	$ 2,396	$ 2,635	$ 4	$ 7,721	$ 7,347	$ (367)	$ (3,883)	$ (3,628)	$ (1,079)	$ (1,079)	$ (5)
Net income	7,340	7,301					7,340	7,301
Other comprehensive income (loss)	248	248							248	248
Convertible debt redemptions (in shares)			11
Convertible debt redemptions	202			202
Dividend to UAL		(1,232)			(1,232)
Share-based compensation	7	7		7	7
Proceeds from exercise of stock options	16			16
UAL contribution related to stock plans		16			16
Repurchases of common stock	(1,232)					(1,232)
Repurchases of common stock (in shares)			(21)
Other	(11)	(12)				(11)					(12)
Ending Balance (in shares) at Dec. 31, 2015			365
Ending Balance at Dec. 31, 2015	8,966	8,963	$ 4	7,946	6,138	(1,610)	3,457	3,673	(831)	(831)	(17)
Net income	2,263	2,264					2,263	2,264
Other comprehensive income (loss)	2	2							2	2
Dividend to UAL		(2,603)			(2,603)
Share-based compensation	32	32		32	32
Proceeds from exercise of stock options	6			6
UAL contribution related to stock plans		6			6
Repurchases of common stock	(2,607)					(2,607)
Repurchases of common stock (in shares)			(50)
Treasury stock retired			$ (1)	(1,415)		3,709	(2,293)
Other	(3)	(58)				(3)					(58)
Ending Balance (in shares) at Dec. 31, 2016			315
Ending Balance at Dec. 31, 2016	8,659	8,606	$ 3	6,569	3,573	(511)	3,427	5,937	(829)	(829)	(75)
Net income	2,131	2,149					2,131	2,149
Other comprehensive income (loss)	(200)	(200)							(200)	(200)
Dividend to UAL		(1,844)			(1,844)
Share-based compensation	56	56		56	56
Proceeds from exercise of stock options	2			2
UAL contribution related to stock plans		2			2
Repurchases of common stock	$ (1,844)					(1,844)
Repurchases of common stock (in shares)	(28)		(28)
Treasury stock retired				(508)		1,576	(1,068)
Net treasury stock issued for share-based awards	$ (12)			(21)		10	(1)
Excess tax benefits from share-based awards	14	14					14	14
Reclassification of stranded tax effects (Note 1)							118	118	(118)	(118)
Other		(15)									(15)
Ending Balance (in shares) at Dec. 31, 2017			287
Ending Balance at Dec. 31, 2017	$ 8,806	$ 8,768	$ 3	$ 6,098	$ 1,787	$ (769)	$ 4,621	$ 8,218	$ (1,147)	$ (1,147)	$ (90)