United Airlines (UAL) 10-K 1 Mar 21 2020 FY Annual report Financial data

Cover Page

Cover Page - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2020	Feb. 24, 2021	Jun. 30, 2020
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-06033
Entity Registrant Name	United Airlines Holdings, Inc.
Entity Address, Address Line One	233 South Wacker Drive,
Entity Address, City or Town	Chicago,
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60606
City Area Code	(872)
Local Phone Number	825-4000
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	36-2675207
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 10
Entity Common Stock, Shares Outstanding		318,476,280
Documents Incorporated by Reference	Certain information required by Items 10, 11, 12 and 13 of Part III of this Form 10-K is incorporated by reference for United Airlines Holdings, Inc. from its definitive proxy statement for its 2021 Annual Meeting of Stockholders.
Document Fiscal Period Focus	FY
Amendment Flag	false
Document Fiscal Year Focus	2020
Entity Central Index Key	0000100517
Common Stock
Document Information [Line Items]
Title of 12(b) Security	Common Stock, $0.01 par value
Trading Symbol	UAL
Security Exchange Name	NASDAQ
Preferred Stock Purchase Rights
Document Information [Line Items]
Title of 12(b) Security	Preferred Stock Purchase Rights
Security Exchange Name	NASDAQ
No Trading Symbol Flag	true
United Airlines, Inc.
Document Information [Line Items]
Entity File Number	001-10323
Entity Registrant Name	United Airlines, Inc.
Entity Address, Address Line One	233 South Wacker Drive,
Entity Address, City or Town	Chicago,
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60606
City Area Code	(872)
Local Phone Number	825-4000
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	74-2099724
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		1,000
Entity Central Index Key	0000319687

Statements of Consolidated Oper

Statements of Consolidated Operations - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating revenue:
Operating revenue	$ 15,355	$ 43,259	$ 41,303
Operating expense:
Salaries and related costs	9,522	12,071	11,458
Aircraft fuel	3,153	8,953	9,307
Depreciation and amortization	2,488	2,288	2,165
Landing fees and other rent	2,127	2,543	2,449
Regional capacity purchase	2,039	2,849	2,649
Aircraft maintenance materials and outside repairs	858	1,794	1,767
Distribution expenses	459	1,651	1,558
Aircraft rent	198	288	433
Special charges (credit)	(2,616)	246	487
Other operating expenses	3,486	6,275	5,801
Total operating expense	21,714	38,958	38,074
Operating income (loss)	(6,359)	4,301	3,229
Nonoperating income (expense):
Interest expense	(1,063)	(731)	(670)
Interest capitalized	71	85	65
Interest income	50	133	101
Unrealized gains (losses) on investments, net	(194)	153	(5)
Miscellaneous, net	(1,327)	(27)	(72)
Total nonoperating expense, net	(2,463)	(387)	(581)
Income (loss) before income taxes	(8,822)	3,914	2,648
Income tax expense (benefit)	(1,753)	905	526
Net income (loss)	$ (7,069)	$ 3,009	$ 2,122
Earnings per share, basic (in dollars per share)	$ (25.30)	$ 11.63	$ 7.70
Earnings per share, diluted (in dollars per share)	$ (25.30)	$ 11.58	$ 7.67
United Airlines, Inc.
Operating revenue:
Operating revenue	$ 15,355	$ 43,259	$ 41,303
Operating expense:
Salaries and related costs	9,522	12,071	11,458
Aircraft fuel	3,153	8,953	9,307
Depreciation and amortization	2,488	2,288	2,165
Landing fees and other rent	2,127	2,543	2,449
Regional capacity purchase	2,039	2,849	2,649
Aircraft maintenance materials and outside repairs	858	1,794	1,767
Distribution expenses	459	1,651	1,558
Aircraft rent	198	288	433
Special charges (credit)	(2,616)	246	487
Other operating expenses	3,484	6,273	5,799
Total operating expense	21,712	38,956	38,072
Operating income (loss)	(6,357)	4,303	3,231
Nonoperating income (expense):
Interest expense	(1,063)	(731)	(670)
Interest capitalized	71	85	65
Interest income	50	133	101
Unrealized gains (losses) on investments, net	(194)	153	(5)
Miscellaneous, net	(1,327)	(27)	(72)
Total nonoperating expense, net	(2,463)	(387)	(581)
Income (loss) before income taxes	(8,820)	3,916	2,650
Income tax expense (benefit)	(1,753)	905	527
Net income (loss)	(7,067)	3,011	2,123
Passenger revenue
Operating revenue:
Operating revenue	11,805	39,625	37,706
Passenger revenue | United Airlines, Inc.
Operating revenue:
Operating revenue	11,805	39,625	37,706
Cargo
Operating revenue:
Operating revenue	1,648	1,179	1,237
Cargo | United Airlines, Inc.
Operating revenue:
Operating revenue	1,648	1,179	1,237
Other operating revenue
Operating revenue:
Operating revenue	1,902	2,455	2,360
Other operating revenue | United Airlines, Inc.
Operating revenue:
Operating revenue	$ 1,902	$ 2,455	$ 2,360

Statements of Consolidated Comp

Statements of Consolidated Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net income (loss)	$ (7,069)	$ 3,009	$ 2,122
Other comprehensive income (loss), net of tax:
Employee benefit plans	(421)	80	342
Investments and other	0	5	(4)
Total other comprehensive income (loss), net of tax	(421)	85	338
Total comprehensive income (loss), net	(7,490)	3,094	2,460
United Airlines, Inc.
Net income (loss)	(7,067)	3,011	2,123
Other comprehensive income (loss), net of tax:
Employee benefit plans	(421)	80	342
Investments and other	0	5	(4)
Total other comprehensive income (loss), net of tax	(421)	85	338
Total comprehensive income (loss), net	$ (7,488)	$ 3,096	$ 2,461

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 11,269	$ 2,762
Short-term investments	414	2,182
Restricted cash	255	0
Receivables, less allowance for credit losses (2020—$78; 2019—$9)	1,295	1,364
Aircraft fuel, spare parts and supplies, less obsolescence allowance (2020—$478; 2019—$425)	932	1,072
Prepaid expenses and other	635	814
Total current assets	14,800	8,194
Operating property and equipment:
Flight equipment	38,218	35,421
Other property and equipment	8,511	7,926
Purchase deposits for flight equipment	1,166	1,360
Total operating property and equipment	47,895	44,707
Less—Accumulated depreciation and amortization	(16,429)	(14,537)
Total operating property and equipment, net	31,466	30,170
Operating lease right-of-use assets	4,537	4,758
Other assets:
Goodwill	4,527	4,523
Intangibles, less accumulated amortization (2020—$1,495; 2019—$1,440)	2,838	3,009
Restricted cash	218	106
Deferred income taxes	131	0
Notes receivable, less allowance for credit losses (2020—$522)	31	671
Investments in affiliates and other, net	1,000	1,180
Total other assets	8,745	9,489
Total assets	59,548	52,611
Current liabilities:
Accounts payable	1,595	2,703
Accrued salaries and benefits	1,960	2,271
Advance ticket sales	4,833	4,819
Frequent flyer deferred revenue	908	2,440
Current maturities of long-term debt	1,911	1,407
Current maturities of operating leases	612	686
Current maturities of finance leases	182	46
Other	724	566
Total current liabilities	12,725	14,938
Long-term debt	24,836	13,145
Long-term obligations under operating leases	4,986	4,946
Long-term obligations under finance leases	224	220
Other liabilities and deferred credits:
Frequent flyer deferred revenue	5,067	2,836
Pension liability	2,460	1,446
Postretirement benefit liability	994	789
Deferred income taxes	0	1,736
Other financial liabilities from sale-leasebacks	1,140	0
Other	1,156	1,024
Total other liabilities and deferred credits	10,817	7,831
Commitments and contingencies
Stockholders' equity:
Preferred stock	0	0
Common stock	4	3
Additional capital invested	8,366	6,129
Stock held in treasury, at cost	(3,897)	(3,599)
Retained earnings	2,626	9,716
Accumulated other comprehensive loss	(1,139)	(718)
Total stockholders' equity	5,960	11,531
Total liabilities and stockholders' equity	59,548	52,611
United Airlines, Inc.
Current assets:
Cash and cash equivalents	11,269	2,756
Short-term investments	414	2,182
Restricted cash	255	0
Receivables, less allowance for credit losses (2020—$78; 2019—$9)	1,295	1,364
Aircraft fuel, spare parts and supplies, less obsolescence allowance (2020—$478; 2019—$425)	932	1,072
Prepaid expenses and other	635	814
Total current assets	14,800	8,188
Operating property and equipment:
Flight equipment	38,218	35,421
Other property and equipment	8,511	7,926
Purchase deposits for flight equipment	1,166	1,360
Total operating property and equipment	47,895	44,707
Less—Accumulated depreciation and amortization	(16,429)	(14,537)
Total operating property and equipment, net	31,466	30,170
Operating lease right-of-use assets	4,537	4,758
Other assets:
Goodwill	4,527	4,523
Intangibles, less accumulated amortization (2020—$1,495; 2019—$1,440)	2,838	3,009
Restricted cash	218	106
Deferred income taxes	103	0
Notes receivable, less allowance for credit losses (2020—$522)	31	671
Investments in affiliates and other, net	1,000	1,180
Total other assets	8,717	9,489
Total assets	59,520	52,605
Current liabilities:
Accounts payable	1,595	2,703
Accrued salaries and benefits	1,960	2,271
Advance ticket sales	4,833	4,819
Frequent flyer deferred revenue	908	2,440
Current maturities of long-term debt	1,911	1,407
Current maturities of operating leases	612	686
Current maturities of finance leases	182	46
Other	728	571
Total current liabilities	12,729	14,943
Long-term debt	24,836	13,145
Long-term obligations under operating leases	4,986	4,946
Long-term obligations under finance leases	224	220
Other liabilities and deferred credits:
Frequent flyer deferred revenue	5,067	2,836
Pension liability	2,460	1,446
Postretirement benefit liability	994	789
Deferred income taxes	0	1,763
Other financial liabilities from sale-leasebacks	1,140	0
Other	1,156	1,025
Total other liabilities and deferred credits	10,817	7,859
Commitments and contingencies
Stockholders' equity:
Common stock	0	0
Additional capital invested	85	0
Retained earnings	4,939	12,353
Accumulated other comprehensive loss	(1,139)	(718)
Payable to (receivable from) parent	2,043	(143)
Total stockholders' equity	5,928	11,492
Total liabilities and stockholders' equity	$ 59,520	$ 52,605

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Receivables, allowance for doubtful accounts	$ 78	$ 9
Aircraft fuel, spare parts and supplies, obsolescence allowance	478	425
Intangibles, accumulated amortization	1,495	$ 1,440
Allowance for credit losses on notes receivable	$ 522
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common shares, authorized (in shares)	1,000,000,000	1,000,000,000
Common shares, outstanding (in shares)	311,845,232	251,216,381
United Airlines, Inc.
Receivables, allowance for doubtful accounts	$ 9	$ 78
Aircraft fuel, spare parts and supplies, obsolescence allowance	425	478
Intangibles, accumulated amortization	1,440	$ 1,495
Allowance for credit losses on notes receivable	$ 522
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common shares, authorized (in shares)	1,000	1,000
Common shares, issued (in shares)	1,000	1,000
Common shares, outstanding (in shares)	1,000	1,000

Statements of Consolidated Cash

Statements of Consolidated Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities:
Net income (loss)	$ (7,069)	$ 3,009	$ 2,122
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities -
Deferred income tax (benefit)	(1,741)	882	512
Depreciation and amortization	2,488	2,288	2,165
Operating and non-operating special charges, non-cash portion	1,448	175	416
Unrealized (gains) losses on investments	194	(153)	5
Other operating activities	320	185	161
Changes in operating assets and liabilities -
Decrease in receivables	135	44	17
(Increase) decrease in other assets	484	(252)	265
Increase in advance ticket sales	14	438	441
Increase in frequent flyer deferred revenue	699	271	222
Increase (decrease) in accounts payable	(1,079)	324	130
Decrease in other liabilities	(26)	(302)	(292)
Net cash provided by (used in) operating activities	(4,133)	6,909	6,164
Investing Activities:
Capital expenditures, net of flight equipment purchase deposit returns	(1,727)	(4,528)	(4,070)
Purchases of short-term and other investments	(552)	(2,897)	(2,552)
Proceeds from sale of short-term and other investments	2,319	2,996	2,616
Loans made to others	0	(174)	(466)
Investment in affiliates	0	(36)	(139)
Other, net	10	79	156
Net cash provided by (used in) investing activities	50	(4,560)	(4,455)
Financing Activities:
Repurchases of common stock	(353)	(1,645)	(1,235)
Proceeds from issuance of debt	16,044	1,847	1,594
Proceeds from equity issuance	2,103	0	0
Payments of long-term debt	(4,383)	(1,240)	(1,727)
Principal payments under finance leases	(66)	(151)	(79)
Capitalized financing costs	(368)	(61)	(37)
Other, net	(20)	(30)	(17)
Net cash provided by (used in) financing activities	12,957	(1,280)	(1,501)
Net increase in cash, cash equivalents and restricted cash	8,874	1,069	208
Cash, cash equivalents and restricted cash at beginning of year	2,868	1,799	1,591
Cash, cash equivalents and restricted cash at end of year	11,742	2,868	1,799
Investing and Financing Activities Not Affecting Cash:
Lease modifications and lease conversions	527	(2)	52
Property and equipment acquired through the issuance of debt, finance leases and other	1,968	515	160
Right-of-use assets acquired through operating leases	198	498	663
Capacity purchase agreement liability converted to debt	33	0	0
Debt associated with termination of a maintenance service agreement	0	0	163
Cash Paid (Refunded) During the Period for:
Interest	874	648	651
Income taxes	(29)	29	19
United Airlines, Inc.
Operating Activities:
Net income (loss)	(7,067)	3,011	2,123
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities -
Deferred income tax (benefit)	(1,741)	882	513
Depreciation and amortization	2,488	2,288	2,165
Operating and non-operating special charges, non-cash portion	1,448	175	416
Unrealized (gains) losses on investments	194	(153)	5
Other operating activities	320	186	162
Changes in operating assets and liabilities -
Decrease in receivables	135	44	17
Increase in intercompany receivables	(14)	(33)	(20)
(Increase) decrease in other assets	484	(252)	265
Increase in advance ticket sales	14	438	441
Increase in frequent flyer deferred revenue	699	271	222
Increase (decrease) in accounts payable	(1,079)	324	130
Decrease in other liabilities	(26)	(302)	(293)
Net cash provided by (used in) operating activities	(4,145)	6,879	6,146
Investing Activities:
Capital expenditures, net of flight equipment purchase deposit returns	(1,727)	(4,528)	(4,070)
Purchases of short-term and other investments	(552)	(2,897)	(2,552)
Proceeds from sale of short-term and other investments	2,319	2,996	2,616
Loans made to others	0	(174)	(466)
Investment in affiliates	0	(36)	(139)
Other, net	10	79	156
Net cash provided by (used in) investing activities	50	(4,560)	(4,455)
Financing Activities:
Proceeds from issuance of debt	16,044	1,847	1,594
Proceeds from equity issuance	2,103	0	0
Payments of long-term debt	(4,383)	(1,240)	(1,727)
Dividend to UAL	(353)	(1,645)	(1,235)
Principal payments under finance leases	(66)	(151)	(79)
Capitalized financing costs	(368)	(61)	(37)
Other, net	(2)	0	1
Net cash provided by (used in) financing activities	12,975	(1,250)	(1,483)
Net increase in cash, cash equivalents and restricted cash	8,880	1,069	208
Cash, cash equivalents and restricted cash at beginning of year	2,862	1,793	1,585
Cash, cash equivalents and restricted cash at end of year	11,742	2,862	1,793
Investing and Financing Activities Not Affecting Cash:
Lease modifications and lease conversions	527	(2)	52
Property and equipment acquired through the issuance of debt, finance leases and other	1,968	515	160
Right-of-use assets acquired through operating leases	198	498	663
Capacity purchase agreement liability converted to debt	33	0	0
Debt associated with termination of a maintenance service agreement	0	0	163
Cash Paid (Refunded) During the Period for:
Interest	874	648	651
Income taxes	$ (29)	$ 29	$ 19

Statements of Consolidated Stoc

Statements of Consolidated Stockholder's Equity - USD ($) $ in Millions		Total		United Airlines, Inc.		Adoption of New Accounting Standard		Adoption of New Accounting StandardUnited Airlines, Inc.	[2]	Common Stock	Additional Capital Invested	Additional Capital InvestedUnited Airlines, Inc.	Treasury Stock	Retained Earnings	Retained EarningsUnited Airlines, Inc.	Retained EarningsAdoption of New Accounting Standard		Retained EarningsAdoption of New Accounting StandardUnited Airlines, Inc.	[2]	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss)United Airlines, Inc.	Accumulated Other Comprehensive Income (Loss)Adoption of New Accounting Standard	(Receivable from) Payable to Related Parties, NetUnited Airlines, Inc.
Balance (in shares) at Dec. 31, 2017										287,000,000
Balance at Dec. 31, 2017		$ 8,788		$ 8,751		$ 0				$ 3	$ 6,098	$ 1,787	$ (769)	$ 4,603	$ 8,201	$ (6)				$ (1,147)	$ (1,147)	$ 6	$ (90)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		2,122		2,123										2,122	2,123
Other comprehensive loss		338		338																338	338
Dividend to UAL				(1,249)								(1,249)
Stock-settled share-based compensation		60		60							60	60
Repurchases of common stock (in shares)										(17,500,000)
Repurchases of common stock		(1,250)											(1,250)
Net treasury stock issued for share-based awards (in shares)										400,000
Net treasury stock issued for share-based awards		(16)									(38)		26	(4)
Other (b)				(19)											(5)						6		(20)
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)		3,009		3,011										3,009	3,011
Other comprehensive loss		85		85																85	85
Dividend to UAL				(1,641)								(664)			(977)
Stock-settled share-based compensation		66		66							66	66
Repurchases of common stock (in shares)										(19,200,000)
Repurchases of common stock		(1,641)											(1,641)
Net treasury stock issued for share-based awards (in shares)										500,000
Net treasury stock issued for share-based awards		$ (30)									(57)		35	(8)
Other (b)				$ (33)											0						0		(33)
Balance (in shares) at Dec. 31, 2019		251,216,381		1,000						251,200,000
Balance at Dec. 31, 2019		$ 11,531		$ 11,492		$ (17)	[1]	$ (17)		$ 3	6,129	0	(3,599)	9,716	12,353	$ (17)	[1]	$ (17)		(718)	(718)		(143)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]		us-gaap:AccountingStandardsUpdate201613Member	[1]	us-gaap:AccountingStandardsUpdate201613Member	[2]
Net income (loss)		$ (7,069)		$ (7,067)										(7,069)	(7,067)
Other comprehensive loss		(421)		(421)																(421)	(421)
Dividend to UAL				(342)								(12)			(330)
Sale of common stock (in shares)										64,600,000
Sale of common stock		2,103								$ 1	2,102
Stock-settled share-based compensation		$ 97		97							97	97
Repurchases of common stock (in shares)		(4,000,000)								(4,400,000)
Repurchases of common stock		$ (342)											(342)
Net treasury stock issued for share-based awards (in shares)										400,000
Net treasury stock issued for share-based awards		(19)									(59)		44	(4)
Warrants issued		$ 97									97
Other (b)	[3]			$ 2,186																			2,186
Balance (in shares) at Dec. 31, 2020		311,845,232		1,000						311,800,000
Balance at Dec. 31, 2020		$ 5,960		$ 5,928						$ 4	$ 8,366	$ 85	$ (3,897)	$ 2,626	$ 4,939					$ (1,139)	$ (1,139)		$ 2,043
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]		us-gaap:AccountingStandardsUpdate201613Member
[1]	Transition adjustment due to the adoption of Accounting Standards Update No. 2016-13, Financial Instruments — Credit Losses
[2]	Transition adjustment due to the adoption of Accounting Standards Update No. 2016-13, Financial Instruments — Credit Losses
[3]	Primarily relates to equity issuances of UAL common stock.

Overview

Overview	12 Months Ended
	Dec. 31, 2020
Unusual or Infrequent Items, or Both [Abstract]
Overview	Overview United Airlines Holdings, Inc. (together with its consolidated subsidiaries, "UAL" or the "Company") is a holding company and its principal, wholly-owned subsidiary is United Airlines, Inc. (together with its consolidated subsidiaries, "United"). As UAL consolidates United for financial statement purposes, disclosures that relate to activities of United also apply to UAL, unless otherwise noted. United's operating revenues and operating expenses comprise nearly 100% of UAL's revenues and operating expenses. In addition, United comprises approximately the entire balance of UAL's assets, liabilities and operating cash flows. When appropriate, UAL and United are named specifically for their individual contractual obligations and related disclosures and any significant differences between the operations and results of UAL and United are separately disclosed and explained. We sometimes use the words "we," "our," "us," and the "Company" in this report for disclosures that relate to all of UAL and United. Recent Developments The novel coronavirus (COVID-19) pandemic, together with the measures implemented or recommended by governmental authorities and private organizations in response to the pandemic, has had an adverse impact that has been material to the Company's business, operating results, financial condition and liquidity. The Company began experiencing a significant decline in international and domestic demand related to COVID-19 during the first quarter of 2020. The decline in demand caused a material deterioration in our revenues in 2020, resulting in a net loss of $7.1 billion. The full extent of the ongoing impact of COVID-19 on the Company's longer-term operational and financial performance will depend on future developments, including those outside our control related to the efficacy and speed of vaccination programs in curbing the spread of the virus, the introduction and spread of new variants of the virus which may be resistant to currently approved vaccines, passenger testing requirements, mask mandates or other restrictions on travel, all of which are highly uncertain and cannot be predicted with certainty In response to decreased demand, the Company cut, relative to 2019 capacity, approximately 57% of its scheduled capacity for 2020. In the first quarter of 2021, the Company expects scheduled capacity to be down at least 51% versus the first quarter of 2019. The Company plans to continue to proactively evaluate and cancel flights on a rolling 60-day basis until it sees signs of a recovery in demand and expects demand to remain suppressed, relative to 2019 levels, until vaccines for COVID-19 are widely distributed and are effective in curbing the spread of the virus. In addition, the Company does not currently expect the recovery from COVID-19 to follow a linear path. As such, the Company's actual flown capacity may differ materially from its currently scheduled capacity. The Company has taken a number of actions in response to the decreased demand for air travel. In addition to the schedule reductions discussed above, the Company has: • reduced its planned capital expenditures and reduced operating expenditures in 2020 (including by postponing projects deemed non-critical to the Company's operations); • terminated its share repurchase program; • issued or entered into approximately $13.4 billion in new secured notes, secured term loan facilities and new aircraft financings in 2020, including short term borrowings that were paid in 2020; • borrowed $1.0 billion under the $2.0 billion revolving credit facility established under the Amended and Restated Credit and Guaranty Agreement (the "Credit Agreement"); • availed itself of financial assistance and/or financing made available by the U.S. Treasury Department ("Treasury"), as further described below; • raised approximately $2.1 billion in cash proceeds from the issuance and sale of UAL common stock in 2020; • entered into agreements to finance certain aircraft currently subject to purchase agreements through sale and leaseback transactions; • elected to defer the payment of $199 million in payroll taxes incurred through December 31, 2020, as provided by the Coronavirus Aid, Relief, and Economic Security Act (the "CARES Act"), until December 2021, at which time 50% is due, with the remaining amount due December 2022; and • taken a number of actions to reduce employee-related costs, including, among other items, the Company's Chief Executive Officer and President waived 100% of their respective base salaries through the end of 2020, other officers temporarily waived a portion of their base salaries, the Company's non-employee directors waived 100% of their cash compensation for the second and third quarters of 2020, the Company suspended merit salary increases for 2020 and implemented a temporary four-day work week for management and administrative employees and the Company offered voluntary unpaid leaves of absence. The Company also entered into an agreement with its pilots to distribute fewer flight hours to a larger number of pilots, while also reaching agreements to provide a path to early retirement and reduce expense through voluntary leave of absence programs. In addition, and as announced in July 2020, the Company started the involuntary furlough process by issuing Worker Adjustment and Retraining Notification ("WARN") Act notices to 36,000 of its employees. Since then, the Company worked to reduce the total number of furloughs to approximately 13,000 employees by working closely with its union partners, introducing new voluntary options selected by approximately 9,000 employees and proposing creative solutions that would save jobs. As a result of the Company's entry into the PSP2 Agreement, as described below, the Company issued recall notices to these furloughed employees and others impacted by furlough mitigation programs. See the discussion below for more detail about the PSP2 Agreement and the recall process. The Company continues to focus on reducing expenses and managing its liquidity. We expect to continue to modify our cost management structure and capacity as the timing of demand recovery becomes more certain. On March 27, 2020, the President of the United States signed the CARES Act into law. The CARES Act is intended to respond to the COVID-19 pandemic and its impact on the economy, public health, state and local governments, individuals, and businesses. The CARES Act also provides supplemental appropriations for federal agencies to respond to the COVID-19 pandemic. On April 20, 2020, United entered into a Payroll Support Program Agreement (the "PSP Agreement") with Treasury providing the Company with total funding of approximately $5.1 billion pursuant to the Payroll Support Program established under the CARES Act. These funds were used to pay for the wages, salaries and benefits of United employees. Approximately $3.6 billion of the $5.1 billion was provided as a direct grant, and approximately $1.5 billion consists of indebtedness evidenced by a 10-year senior unsecured promissory note (the "PSP Note"). See Note 2 of this report for additional information related to warrants issued in connection with the PSP Note and Note 10 of this report for a discussion of the PSP Note. During 2020, UAL and United entered into a loan and guarantee agreement with Treasury. The agreement provides for a term loan facility of up to approximately $7.5 billion (the "CARES Act Term Loan Facility") pursuant to the loan program established under Section 4003(b)(1) of the CARES Act (the "Loan Program"). The loans (the "CARES Act Term Loans") may be disbursed in up to three disbursements on or before May 28, 2021. On September 28, 2020, United borrowed, and recorded as Long-term debt on the Company's consolidated balance sheet, $520 million under the CARES Act Term Loan Facility, the proceeds of which were used to pay certain transaction fees and expenses and for working capital and other general corporate purposes of the Company. See Note 2 of this report for additional information related to warrants issued in connection with the CARES Act Term Loans and Note 10 of this report for a discussion of the CARES Act Term Loans. Under the PSP Agreement and the Loan Program, the Company and its business are subject to certain restrictions, including, but not limited to, restrictions on the payment of dividends and the ability to repurchase UAL's equity securities, requirements to maintain certain levels of scheduled service and certain limitations on executive compensation. On January 15, 2021, United entered into a Payroll Support Agreement (the "PSP2 Agreement") with Treasury providing the Company with total funding of approximately $2.6 billion, pursuant to the Payroll Support Program established under Subtitle A of Title IV of Division N of the Consolidated Appropriations Act, 2021 (the "PSP Extension Law"). These funds were used to pay for the wages, salaries and benefits of United employees, including the payment of lost wages, salaries and benefits to returning employees. Approximately $1.9 billion was provided as a direct grant and approximately $753 million consists of indebtedness evidenced by a 10-year senior unsecured promissory note (the "PSP2 Note"). As of February 25, 2021, we have received a total of $1.3 billion. See Note 2 of this report for additional information on warrants issued in connection with the PSP2 Note and Note 10 of this report for a discussion of the PSP2 Note. Pursuant to the PSP2 Agreement, the Company is required to comply with certain provisions of the PSP Extension Law, including, among others, the requirement that all funds provided under the Payroll Support Program will be used by United exclusively for the continuation of payment of its U.S. employee wages, salaries and benefits, including the payment of lost wages, salaries and benefits to returning U.S. employees; requirements to maintain U.S. employment levels from the date of the PSP2 Agreement through March 31, 2021; requirements to recall (as such term is defined in the PSP2 Agreement), any U.S. employees subject to involuntary termination or furlough between October 1, 2020 and the date of the PSP2 Agreement, compensate such returning employees for certain lost salary, wages and benefits between December 1, 2020 and the date of the PSP2 Agreement and restore certain rights and protections for such returning employees; provisions prohibiting certain reductions in U.S. employee wages, salaries and benefits; provisions prohibiting the payment of dividends and the repurchase of certain equity until March 31, 2022; and provisions restricting the payment of certain executive compensation until October 1, 2022. As a result of the PSP2 Agreement, the Company offered employment, through March 2021, to employees who were impacted by involuntary furloughs. Because the Company cannot predict with certainty whether it will receive further payroll support from the federal government or when demand for air travel will increase in the short term, the Company is preparing for the possibility that these recalled employees might again be furloughed as soon as the end of the first quarter of 2021. The Company may record additional costs associated with these actions in the first quarter of 2021. Also, in order to reduce the number of such furloughs, during the first quarter of 2021, the Company offered voluntary leave and other programs to certain of its frontline employees, the cost of which cannot be estimated at this time.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Significant Accounting Policies	SIGNIFICANT ACCOUNTING POLICIES (a) Use of Estimates— The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America ("GAAP") requires management to make estimates and assumptions that affect the amounts reported in these financial statements and accompanying notes. Actual results could differ from those estimates. (b) Revenue Recognitio n— The Company presents Passenger revenue, Cargo revenue and Other operating revenue on its income statement. Passenger revenue is recognized when transportation is provided and Cargo revenue is recognized when shipments arrive at their destination. Other operating revenue is recognized as the related performance obligations are satisfied. Passenger tickets and related ancillary services sold by the Company for flights are purchased primarily via credit card transactions, with payments collected by the Company in advance of the performance of related services. The Company initially records ticket sales in its Advance ticket sales liability, deferring revenue recognition until the travel occurs. For travel that has more than one flight segment, the Company deems each segment as a separate performance obligation and recognizes revenue for each segment as travel occurs. Tickets sold by other airlines where the Company provides the transportation are recognized as passenger revenue at the estimated value to be billed to the other airline when travel is provided. Differences between amounts billed and the actual amounts may be rejected and rebilled or written off if the amount recorded was different from the original estimate. When necessary, the Company records a reserve against its billings and payables with other airlines based on historical experience. The Company sells certain tickets with connecting flights with one or more segments operated by its other airline partners. For segments operated by its other airline partners, the Company has determined that it is acting as an agent on behalf of the other airlines as they are responsible for their portion of the contract (i.e. transportation of the passenger). The Company, as the agent, recognizes revenue within Other operating revenue at the time of the travel for the net amount representing commission to be retained by the Company for any segments flown by other airlines. Refundable tickets expire after one year from the date of issuance. Non-refundable tickets generally expire on the date of the intended travel, unless the date is extended by notification from the customer on or before the intended travel date. In April 2020, due to the COVID-19 pandemic, the Company extended the expiration dates on all passenger tickets issued between May 1, 2019 and March 31, 2020 to 24 months from the original issue date. On February 24, 2021, the Company extended the expiration dates for all tickets issued between May 1, 2019 and March 31, 2021 to March 31, 2022. Fees charged in association with changes or extensions to non-refundable tickets are considered part of the Company's passenger travel obligation. As such, those fees are deferred at the time of collection and recognized at the time the travel is provided. Effective August 30, 2020, the Company eliminated change fees on all standard Economy and Premium cabin tickets for travel within the 50 U.S. states, Washington, D.C., Puerto Rico and the U.S. Virgin Islands. Also, in December 2020, the Company eliminated change fees on flights from the U.S. to all international destinations and fees on Basic Economy and all other international travel tickets issued by March 31, 2021. United initially capitalizes the costs of selling airline travel tickets and then recognizes those costs as Distribution expense at the time of travel. Passenger ticket costs include credit card fees, travel agency and other commissions paid, as well as global distribution systems booking fees. Advance Ticket Sales. Advance ticket sales represent the Company's liability to provide air transportation in the future. All tickets sold at any given point of time have travel dates extending up to 12 months. The Company defers amounts related to future travel in its Advance ticket sales liability account. The Company's Advance ticket sales liability also includes credits issued to customers on electronic travel certificates ("ETCs") and future flight credits ("FFCs"), primarily for ticket cancellations, which can be applied towards a purchase of a new ticket. In April 2020, due to the COVID-19 pandemic, the Company extended the expiration dates of ETCs from 12 months from the date of issuance to 24 months from the date of issuance and extended the expiration of FFCs, for tickets issued between May 1, 2019 and March 31, 2020 to 24 months from the original issue date. On February 24, 2021, the Company extended the expiration dates for all tickets issued between May 1, 2019 and March 31, 2021 to March 31, 2022. As of December 31, 2020, the Company's Advance ticket sales liability included $3.1 billion related to these credits and approximately 74% of these credits have expiration dates extending beyond 12 months. The Company records breakage revenue on the travel date for its estimate of tickets that will expire unused. To determine breakage, the Company uses its historical experience with refundable and nonrefundable expired tickets and other facts, such as recent aging trends, program changes and modifications that could affect the ultimate expiration patterns of tickets. The Company continues to use its historical experience and most recent trends and program changes to estimate its breakage. The Company will update its breakage estimates as future information is received. Given the uncertainty of travel demand caused by COVID-19, a significant portion of the $3.1 billion related to the ETCs and FFCs may expire unused in future periods and get recognized as breakage. Also, the Company is unable to estimate the amount of the ETCs and FFCs that will be used within the next 12 months and has classified the entire amount of the Advanced ticket liability in current liabilities even though some of the ETCs and FFCs could be used after the next 12 months. In the years ended December 31, 2020, 2019 and 2018, the Company recognized approximately $3.0 billion, $3.4 billion and $3.1 billion, respectively, of passenger revenue for tickets that were included in Advance ticket sales at the beginning of those periods. Revenue by Geography. The Company further disaggregates revenue by geographic regions. Operating segments are defined as components of an enterprise with separate financial information, which are evaluated regularly by the chief operating decision maker and are used in resource allocation and performance assessments. The Company deploys its aircraft across its route network through a single route scheduling system to maximize its value. When making resource allocation decisions, the Company's chief operating decision maker evaluates flight profitability data, which considers aircraft type and route economics. The Company's chief operating decision maker makes resource allocation decisions to maximize the Company's consolidated financial results. Managing the Company as one segment allows management the opportunity to maximize the value of its route network. The Company's operating revenue by principal geographic region (as defined by the U.S. Department of Transportation) for the years ended December 31 is presented in the table below (in millions): 2020 2019 2018 Domestic (U.S. and Canada) $ 9,911 $ 26,960 $ 25,552 Atlantic 2,226 7,387 7,103 Pacific 1,706 5,132 5,188 Latin America 1,512 3,780 3,460 Total $ 15,355 $ 43,259 $ 41,303 The Company attributes revenue among the geographic areas based upon the origin and destination of each flight segment. The Company's operations involve an insignificant level of revenue-producing assets in geographic regions as the overwhelming majority of the Company's revenue-producing assets (primarily U.S. registered aircraft) can be deployed in any of its geographic regions. Ancillary Fees. The Company charges fees, separately from ticket sales, for certain ancillary services that are directly related to passengers' travel, such as ticket change fees, baggage fees, inflight amenities fees, and other ticket-related fees. These ancillary fees are part of the travel performance obligation and, as such, are recognized as passenger revenue when the travel occurs. The Company recorded $918 million, $2.4 billion and $2.2 billion of ancillary fees within passenger revenue in the years ended December 31, 2020, 2019 and 2018, respectively. (c) Ticket Taxes— Certain governmental taxes are imposed on the Company's ticket sales through a fee included in ticket prices. The Company collects these fees and remits them to the appropriate government agency. These fees are recorded on a net basis and, as a result, are excluded from revenue. The CARES Act provided an excise tax holiday that suspended certain U.S. aviation excise taxes. The excise tax holiday began on March 28, 2020 and ended on December 31, 2020. During the excise tax holiday, no excise tax was imposed on amounts paid for the transportation of persons and property by air. At December 31, 2020, the Company had approximately $150 million of excise taxes refunded to customers that are to be reimbursed by the U.S. government in 2021. (d) Frequent Flyer Accounting— United's MileagePlus loyalty program builds customer loyalty by offering awards, benefits and services to program participants. Members in this program earn miles for travel on United, United Express, Star Alliance members and certain other airlines that participate in the program. Members can also earn miles by purchasing goods and services from our network of non-airline partners. We have contracts to sell miles to these partners with the terms extending from one Miles Earned in Conjunction with Travel. When frequent flyers earn miles for flights, the Company recognizes a portion of the ticket sales as revenue when the travel occurs and defers a portion of the ticket sale representing the value of the related miles as a separate performance obligation. The Company determines the estimated selling price of travel and miles as if each element is sold on a separate basis. The total consideration from each ticket sale is then allocated to each of these elements, individually, on a pro-rata basis. At the time of travel, the Company records the portion allocated to the miles to Frequent flyer deferred revenue on the Company's consolidated balance sheet and subsequently recognizes it into revenue when miles are redeemed for air travel and non-air travel awards. Estimated Selling Price of Miles . The Company's estimated selling price of miles is based on an equivalent ticket value, which incorporates the expected redemption of miles, as the best estimate of selling price for these miles. The equivalent ticket value is based on the prior 12 months' weighted average equivalent ticket value of similar fares as those used to settle award redemptions while taking into consideration such factors as redemption pattern, cabin class, loyalty status and geographic region. The estimated selling price of miles is adjusted by breakage that considers a number of factors, including redemption patterns of various customer groups. Estimate of Miles Not Expected to be Redeemed ("Breakage") . The Company's breakage model is based on the assumption that the likelihood that an account will redeem its miles can be estimated based on a consideration of the account's historical behavior. The Company uses a logit regression model to estimate the probability that an account will redeem its current miles balance. The Company reviews its breakage estimates annually based upon the latest available information. The Company's estimate of the expected breakage of miles requires significant management judgment. Current and future changes to breakage assumptions, or to program rules and program redemption opportunities, may result in material changes to the deferred revenue balance as well as recognized revenues from the program. For the portion of the outstanding miles that we estimate will not be redeemed, we recognize the associated value proportionally as the remaining miles are redeemed. Co-Brand Agreement . During 2020, the Company entered into a Third Amended and Restated Co-Branded Card Marketing Services Agreement (as amended from time to time, the "Co-Brand Agreement") with its co-branded credit card partner JPMorgan Chase Bank, N.A. ("Chase"). The Co-Brand Agreement extended the term of the agreement into 2029 and modified certain other terms, resulting in a different allocation among the separately identifiable performance obligations. Chase awards miles to MileagePlus members based on their credit card activity. United identified the following significant separately identifiable performance obligations in the Co-Brand Agreement: • MileagePlus miles awarded – United has a performance obligation to provide MileagePlus cardholders with miles to be used for air travel and non-travel award redemptions. The Company records Passenger revenue related to the travel awards when the transportation is provided and records Other revenue related to the non-travel awards when the goods or services are delivered. The Company records the cost associated with non-travel awards in Other operating revenue, as an agent. • Marketing – United has a performance obligation to provide Chase access to United's customer list and the use of United's brand. Marketing revenue is recorded to Other operating revenue as miles are delivered to Chase. • Advertising – United has a performance obligation to provide advertising in support of the MileagePlus card in various customer contact points such as United's website, email promotions, direct mail campaigns, airport advertising and in-flight advertising. Advertising revenue is recorded to Other operating revenue as miles are delivered to Chase. • Other travel-related benefits – United's performance obligations are comprised of various items such as waived bag fees, seat upgrades and lounge passes. Lounge passes are recorded to Other operating revenue as customers use the lounge passes. Bag fees and seat upgrades are recorded to Passenger revenue at the time of the associated travel. We account for all the payments received (including monthly and one-time payments) under the Co-Brand Agreement by allocating them to the separately identifiable performance obligations. The fair value of the separately identifiable performance obligations is determined using management's estimated selling price of each component. The objective of using the estimated selling price based methodology is to determine the price at which we would transact a sale if the product or service were sold on a stand-alone basis. Accordingly, we determine our best estimate of selling price by considering multiple inputs and methods including, but not limited to, discounted cash flows, brand value, volume discounts, published selling prices, number of miles awarded and number of miles redeemed. The Company estimated the selling prices and volumes over the term of the Co-Brand Agreement in order to determine the allocation of proceeds to each of the components to be delivered. We also evaluate volumes on an annual basis, which may result in a change in the allocation of the estimated consideration from the Co-Brand Agreement on a prospective basis. Frequent Flyer Deferred Revenue. Miles in MileagePlus members' accounts are combined into one homogeneous pool and are thus not separately identifiable, for award redemption purposes, between miles earned in the current period and those in their beginning balance. Of the miles expected to be redeemed, the majority of these miles have historically been redeemed within two years. The table below presents a roll forward of Frequent flyer deferred revenue (in millions): Twelve Months Ended 2020 2019 Total Frequent flyer deferred revenue - beginning balance $ 5,276 $ 5,005 Total miles awarded 1,336 2,621 Travel miles redeemed (Passenger revenue) (568) (2,213) Non-travel miles redeemed (Other operating revenue) (69) (137) Total Frequent flyer deferred revenue - ending balance $ 5,975 $ 5,276 In the years ended December 31, 2020, 2019 and 2018, the Company recognized, in Other operating revenue, $1.7 billion, $2.0 billion and $2.0 billion (including a one-time $50 million payment), respectively, related to the marketing, advertising, non-travel miles redeemed (net of related costs) and other travel-related benefits of the mileage revenue associated with our various partner agreements including, but not limited to, our Chase co-brand agreement. The portion related to the MileagePlus miles awarded of the total amounts received is deferred and presented in the table above as an increase to the frequent flyer liability. We determine the current portion of our frequent flyer liability based on expected redemptions in the next 12 months. Given the uncertainty in travel demand caused by COVID-19, we currently estimate a greater percentage of award redemptions will occur beyond 12 months, however this estimate may change as travel demand and award redemptions change in future periods. (e) Cash and Cash Equivalents and Restricted Cash— Highly liquid investments with a maturity of three months or less on their acquisition date are classified as cash and cash equivalents. Restricted cash-current— primarily includes $217 million cash collateral for a standby letter of credit associated with guarantees under the BRW Term Loan. See Note 8 of this report for additional information on the BRW Term Loan and Note 13 for additional information on the guarantee. The balance also includes amounts to be used for the payment of fees, principal and interest on the $6.8 billion of senior secured notes and a secured term loan facility (the "MileagePlus Financing") secured by substantially all of the assets of Mileage Plus Holdings, LLC ("MPH"), a direct wholly-owned subsidiary of United. Restricted cash-non-current— primarily includes collateral associated with the MileagePlus Financing, collateral for letters of credit and collateral associated with facility leases and other insurance-related obligations. Restricted cash is classified as short-term or long-term in the consolidated balance sheets based on the expected timing of return of the assets to the Company or payment to an outside party. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the consolidated balance sheets that sum to the total of the same such amounts shown in the statements of consolidated cash flows (in millions): UAL United At December 31, At December 31, 2020 2019 2018 2020 2019 2018 Current assets: Cash and cash equivalents $ 11,269 $ 2,762 $ 1,694 $ 11,269 $ 2,756 $ 1,688 Restricted cash 255 — — 255 — — Other assets: Restricted cash 218 106 105 218 106 105 Total cash, cash equivalents and restricted cash shown in the statement of consolidated cash flows $ 11,742 $ 2,868 $ 1,799 $ 11,742 $ 2,862 $ 1,793 (f) Investments— Debt investments are classified as available-for-sale and are stated at fair value. Realized gains and losses on sales of these investments are reflected in Miscellaneous, net in the consolidated statements of operations. Unrealized gains and losses on available-for-sale securities are reflected as a component of accumulated other comprehensive income (loss). Equity investments with readily determinable fair values are measured at fair value. Equity investments without readily determinable fair values are measured using the equity method, or measured at cost with adjustments for observable changes in price or impairments (referred to as the measurement alternative). Changes in fair value are recorded in Unrealized gains (losses) on investments, net in the consolidated statements of operations. See Note 9 of this report for additional information related to investments. (g) Accounts Receivable— Accounts receivable primarily consist of amounts due from credit card companies, non-airline partners, and cargo customers. We provide an allowance for uncollectible accounts equal to the estimated losses expected to be incurred based on historical write-offs and other specific analyses. Bad debt expense and write-offs related to trade receivables were not material for the year ended December 31, 2020 and 2019. (h) Aircraft Fuel, Spare Parts and Supplies— The Company accounts for aircraft fuel, spare parts and supplies at average cost and provides an obsolescence allowance for aircraft spare parts with an assumed residual value of 10% of original cost. (i) Property and Equipment— The Company records additions to owned operating property and equipment at cost when acquired. Property under finance leases and the related obligation for future lease payments are recorded at an amount equal to the initial present value of those lease payments. Modifications that enhance the operating performance or extend the useful lives of airframes or engines are capitalized as property and equipment. We periodically receive credits in connection with the acquisition of aircraft and engines including those related to contractual damages related to delays in delivery. These credits are deferred until the aircraft and engines are delivered, and then applied as a reduction to the cost of the related equipment. Depreciation and amortization of owned depreciable assets is based on the straight-line method over the assets' estimated useful lives. Leasehold improvements are amortized over the remaining term of the lease, including estimated facility renewal options when renewal is reasonably certain at key airports, or the estimated useful life of the related asset, whichever is less. Properties under finance leases are amortized on the straight-line method over the life of the lease or, in the case of certain aircraft, over their estimated useful lives, whichever is shorter. Amortization of finance lease assets is included in depreciation and amortization expense. The estimated useful lives of property and equipment are as follows: Estimated Useful Life (in years) Aircraft, spare engines and related rotable parts 25 to 30 Aircraft seats 10 to 15 Buildings 25 to 45 Other property and equipment 3 to 15 Computer software 5 to 15 Building improvements 1 to 40 As of December 31, 2020 and 2019, the Company had a carrying value of computer software of $548 million and $422 million, respectively. For the years ended December 31, 2020, 2019 and 2018, the Company's depreciation expense related to computer software was $172 million, $135 million and $122 million, respectively. Aircraft and aircraft spare parts were assumed to have residual values of approximately 10% of original cost, and other categories of property and equipment were assumed to have no residual value. (j) Long-Lived Asset Impairments— The Company evaluates the carrying value of long-lived assets subject to amortization whenever events or changes in circumstances indicate that an impairment may exist. For purposes of this testing, the Company has generally identified the aircraft fleet type as the lowest level of identifiable cash flows for its mainline fleet and the contract level for its regional fleet under capacity purchase agreements ("CPAs"). An impairment charge is recognized when the asset's carrying value exceeds its net undiscounted future cash flows. The amount of the charge is the difference between the asset's carrying value and fair market value. In December 2020, the Company decided to permanently ground 11 Boeing 757-200 aircraft and recorded $94 million in impairment changes. See Note 14 of this report for additional information related to impairments. (k) Intangibles— The Company has finite-lived and indefinite-lived intangible assets, including goodwill. Finite-lived intangible assets are amortized over their estimated useful lives. Goodwill and indefinite-lived intangible assets are not amortized but are reviewed for impairment on an annual basis as of October 1, or more frequently if events or circumstances indicate that the asset may be impaired. We value goodwill and indefinite-lived intangible assets primarily using market and income approach valuation techniques. These measurements include the following key assumptions: (1) forecasted revenues, expenses and cash flows, (2) terminal period revenue growth and cash flows, (3) an estimated weighted average cost of capital, (4) assumed discount rates depending on the asset and (5) a tax rate. These assumptions are consistent with those that hypothetical market participants would use. Because we are required to make estimates and assumptions when evaluating goodwill and indefinite-lived intangible assets for impairment, actual transaction amounts may differ materially from these estimates. In each quarter of 2020, the Company evaluated its goodwill and intangible assets for possible impairments due to the impact of the COVID-19 pandemic on UAL's market capitalization and cash flow projections. For goodwill and certain of its intangible assets, including the Company's China routes, London-Heathrow slots, alliances and the United trade name and logo, the Company performed a quantitative assessment which involved determining the fair value of the asset and comparing that amount to the asset's carrying value and, in the case of goodwill, comparing the Company's fair value to its carrying value. For all other intangible assets, the Company performed a qualitative assessment of whether it was more likely than not that an impairment had occurred. To determine fair value, the Company used discounted cash flow methods appropriate for each asset. Key inputs into the models included forecasted capacity, revenues, fuel costs, other operating costs and an overall discount rate. The assumptions used for future projections include that demand will likely remain suppressed through 2021. These assumptions are inherently uncertain as they relate to future events and circumstances. See Note 14 of this report for additional information related to impairments. The following table presents information about the Company's goodwill and other intangible assets at December 31 (in millions): 2020 2019 Gross Accumulated Gross Accumulated Goodwill $ 4,527 $ 4,523 Indefinite-lived intangible assets Route authorities $ 1,020 $ 1,150 Airport slots 560 546 Tradenames and logos 593 593 Alliances 404 404 Total $ 2,577 $ 2,693 Finite-lived intangible assets Frequent flyer database $ 1,177 $ 971 $ 1,177 $ 931 Hubs 145 111 145 104 Contracts 120 116 120 111 Other 314 297 314 294 Total $ 1,756 $ 1,495 $ 1,756 $ 1,440 Amortization expense in 2020, 2019 and 2018 was $55 million, $60 million and $67 million, respectively. Projected amortization expense in 2021, 2022, 2023, 2024 and 2025 is $50 million, $40 million, $37 million, $32 million and $28 million, respectively. (l) Labor Costs— The Company records expenses associated with new or amendable labor agreements when the amounts are probable and estimable. These include costs associated with lump sum cash payments that would be made in conjunction with the ratification of labor agreements. To the extent these upfront costs are in lieu of future pay increases, they would be capitalized and amortized over the term of the labor agreements. If not, these amounts would be expensed. (m) Share-Based Compensation— The Company measures the cost of employee services received in exchange for an award of equity instruments based on the grant date fair value of the award. The resulting cost is recognized over the period during which an employee is required to provide service in exchange for the award, usually the vesting period. Obligations for cash-settled restricted stock units ("RSUs") are remeasured at fair value throughout the requisite service period at the close of the reporting period based upon UAL's stock price. In addition to the service requirement, certain RSUs have performance metrics that must be achieved prior to vesting. These awards are accrued based on the expected level of achievement at each reporting period. An adjustment is recorded each reporting period to adjust compensation expense based on the then current level of expected performance achievement for the performance-based awards. See Note 4 of this report for additional information on UAL's share-based compensation plans. (n) Maintenance and Repairs— The cost of maintenance and repairs, including the cost of minor replacements, is charged to expense as incurred, except for costs incurred under our power-by-the-hour ("PBTH") engine maintenance agreements. PBTH contracts transfer certain risk to third-party service providers and fix the amount we pay per flight hour or per cycle to the service provider in exchange for maintenance and repairs under a predefined maintenance program. Under PBTH agreements, the Company recognizes expense at a level rate per engine hour, unless the level of service effort and the related payments during the period are substantially consistent, in which case the Company recognizes expense based on the amounts paid. (o) Advertising— Advertising costs, which are included in Other operating expenses, are expensed as incurred. Advertising expenses were $87 million, $212 million and $211 million for the years ended December 31, 2020, 2019 and 2018, respectively. (p) Third-Party Business— The Company has third-party business revenue that includes catering, ground handling, maintenance services and frequent flyer award non-travel redemptions. Third-party business revenue is recorded in Other operating revenue. The Company also incurs third-party business expenses, such as maintenance, ground handling and catering services for third parties and non-travel mileage redemptions. The third-party business expenses are recorded in Other operating expenses, except for non-travel mileage redemption. Non-travel mileage redemption expenses are recorded to Other operating revenue. (q) Uncertain Income Tax Positions— The Company has recorded reserves for income taxes and associated interest that may become payable in future years. Although management believes that its positions taken on income tax matters are reasonable, the Company nevertheless established tax and interest reserves in recognition that various taxing authorities may challenge certain of the positions taken by the Company, potentially resulting in additional liabilities for taxes and interest. The Company's uncertain tax position reserves are reviewed periodically and are adjusted as events occur that affect its estimates, such as the availability of new information, the lapsing of applicable statutes of limitation, the conclusion of tax audits, the measurement of additional estimated liability, the identification of new tax matters, the release of administrative tax guidance affecting its estimates of tax liabilities, or the rendering of relevant court decisions. The Company records penalties and interest relating to uncertain tax positions as part of income tax expense in its consolidated statements of operations. See Note 6 of this report for additional information on UAL's uncertain tax positions. (r) Recently Issued Accounting Standards— The Company adopted Accounting Standards Update No. 2016-13 Financial Instruments—Credit Losses ("ASU 2016-13") effective January 1, 2020. ASU 2016-13 replaces the incurred loss methodology with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to calculate credit loss estimates. For trade receivables, loans and held-to-maturity debt securities, entities are required to estimate lifetime expected credit losses. For available-for-sale debt securities, entities are required to recognize an allowance for credit losses rather than a reduction to the carrying value of the asset. The Company recorded a $17 million cumulative-effect adjustment, net of related income taxes, to its retained earnings balance on January 1, 2020 as a result of this adoption. See Notes 8, 13 and 14 of this report for additional disclosures about the impact of ASU 2016-13 on 2020 results.

Common Stockholders' Equity and

Common Stockholders' Equity and Preferred Securities	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Common Stockholders' Equity and Preferred Securities	COMMON STOCKHOLDERS' EQUITY AND PREFERRED SECURITIES On February 24, 2020, the Company suspended share repurchases under its share repurchase program authorized by UAL's Board of Directors in July 2019. UAL's Board of Directors subsequently terminated this share repurchase program on April 24, 2020. In 2020, UAL repurchased approximately 4 million shares of UAL common stock in open market transactions for $0.3 billion. See Part II, Item 5, Market for Registrant's Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities, of this report for additional information. On April 20, 2020, UAL entered into a warrant agreement with Treasury, pursuant to which UAL agreed to issue to Treasury warrants to purchase up to approximately 4.6 million shares of common stock, pro rata in conjunction with increases to the principal amount outstanding under the PSP Note (the "PSP Warrants"), with an initial issuance of warrants to purchase up to approximately 2.3 million shares of common stock. As of December 31, 2020, UAL has issued PSP Warrants to purchase up to approximately 4.8 million shares of common stock, with such warrants accounted for as equity instruments. The PSP Warrants have a strike price of $31.50 per share (which was the closing price of UAL's common stock on The Nasdaq Stock Market on April 9, 2020). The PSP Warrants will expire five years after issuance, and are exercisable either through net share settlement, in cash or in shares of UAL common stock, at UAL's option. The relative fair value of the PSP Warrants was calculated using a Black-Scholes options pricing model and approximately $66 million was recorded within stockholders' equity with an offset to the CARES Act grant credit. The PSP Warrants contain customary anti-dilution provisions and registration rights and are freely transferable. Pursuant to the terms of the PSP Warrants, PSP Warrant holders do not have any voting rights. In connection with the entry into the Term Loan Facility, UAL entered into a warrant agreement with Treasury on September 28, 2020, pursuant to which UAL will issue to Treasury warrants (the "Credit Agreement Warrants") to purchase up to approximately 16.4 million shares of UAL common stock, assuming United borrows the initial commitments under the Term Loan Facility in full. The Credit Agreement Warrants will be issued on the date of disbursement of each Term Loan in an amount corresponding to 10% of the principal amount of each such disbursement. In connection with United's borrowing of the initial $520 million loan, on September 28, 2020, UAL issued Credit Agreement Warrants to purchase up to approximately 1.7 million shares of UAL common stock. The Credit Agreement Warrants will have a strike price of $31.50 per share. The Credit Agreement Warrants will expire five years after issuance, and are exercisable either through net share settlement in cash or in shares of UAL common stock, at UAL's option. The relative fair value of the Credit Agreement Warrants was calculated using a Black-Scholes options pricing model and approximately $30 million was recorded within stockholders' equity and as a debt discount against the outstanding loan. If Treasury increases its loan commitments, then the maximum amount of common stock for which warrants could be issued would increase proportionally with such increase to the commitments. During the first quarter of 2021, UAL entered into a warrant agreement with Treasury pursuant to which UAL will issue to Treasury warrants to purchase up to approximately 1.7 million shares of UAL common stock, pro rata in conjunction with increases to the principal amount outstanding under the PSP2 Note (the "PSP2 Warrants"). The PSP2 Warrants will have a strike price of $43.26 per share. The PSP2 Warrants will expire five years after issuance, and are exercisable either through net share settlement in cash or in shares of UAL common stock, at UAL's option. The PSP2 Warrants contain customary anti-dilution provisions, registration rights and are freely transferable. Pursuant to the terms of the PSP2 Warrants, PSP2 Warrant holders do not have any voting rights. In 2020, UAL entered into an underwriting agreement (the "Underwriting Agreement") with Morgan Stanley & Co. LLC and Barclays Capital Inc. (collectively, the "Underwriters"), relating to the issuance and sale by UAL of approximately 43 million shares of its common stock, par value $0.01 per share, at a price to the public of $26.50 per share, resulting in total proceeds of approximately $1.1 billion. On June 15, 2020, UAL entered into an equity distribution agreement (the "Distribution Agreement") with Citigroup Global Markets Inc., BofA Securities, Inc. and J.P. Morgan Securities LLC (collectively, the "Managers"), relating to the issuance and sale from time to time by UAL (the "ATM Offering"), through the Managers, of up to 28 million shares of UAL's common stock, par value $0.01 per share. Sales of the shares, if any, under the Distribution Agreement may be made in any transactions that are deemed to be "at the market offerings" as defined in Rule 415 under the Securities Act of 1933, as amended. Under the terms of the Distribution Agreement, UAL may also sell shares to any Manager, as principal for its own account, at a price agreed upon at the time of sale. If UAL sells shares to a Manager as principal, UAL will enter into a separate agreement with such Manager. As of December 31, 2020, approximately 21.4 million shares were sold in the ATM Offering at an average price of $46.70 per share, with net proceeds to the Company totaling approximately $989 million. At December 31, 2020, approximately 6 million shares of UAL's common stock were reserved for future issuance related to the issuance of equity-based awards under the Company's incentive compensation plans.

Earnings (Loss) Per Share

Earnings (Loss) Per Share	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Earnings (Loss) Per Share	EARNINGS (LOSS) PER SHARE The computations of UAL's basic and diluted earnings (loss) per share are set forth below for the years ended December 31 (in millions, except per share amounts): 2020 2019 2018 Earnings (loss) available to common stockholders $ (7,069) $ 3,009 $ 2,122 Basic weighted-average shares outstanding 279.4 258.8 275.5 Effect of share-based awards — 1.1 1.2 Diluted weighted-average shares outstanding 279.4 259.9 276.7 Earnings (loss) per share, basic $ (25.30) $ 11.63 $ 7.70 Earnings (loss) per share, diluted $ (25.30) $ 11.58 $ 7.67 The number of antidilutive securities excluded from the computation of diluted per share amounts was not material.

Share-Based Compensation Plans

Share-Based Compensation Plans	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Share-Based Compensation Plans	SHARE-BASED COMPENSATION PLANS UAL maintains share-based compensation plans for our management employees and our non-employee directors. These plans provide for grants of non-qualified stock options, incentive stock options (within the meaning of Section 422 of the Internal Revenue Code of 1986), stock appreciation rights, restricted shares, RSUs, performance compensation awards, performance units, cash incentive awards, other equity-based and equity-related awards, and dividends and dividend equivalents. All awards are recorded as either equity or a liability in the Company's consolidated balance sheets. The share-based compensation expense is recorded in salaries and related costs. During 2020, UAL granted share-based compensation awards pursuant to the United Continental Holdings, Inc. 2017 Incentive Compensation Plan. These share-based compensation awards included approximately 2.5 million RSUs consisting of 2.2 million time-vested RSUs and 0.3 million performance-based RSUs. The time-vested RSUs vest pro-rata, typically on February 28th of each year, over a three-year period from the date of grant. The amount of performance-based RSUs vest upon the achievement of established goals based on the Company's absolute pre-tax margin performance as well as a customer metric based on the Company's relative quarterly average of net promoter scores as compared to a group of industry peers, both of which are measured for the three-year performance period ending December 31, 2022. RSUs are generally equity awards settled in stock for domestic employees and liability awards settled in cash for international employees. The cash payments are based on the 20-day average closing price of UAL common stock immediately prior to the vesting date. The following table provides information related to UAL's share-based compensation plan cost for the years ended December 31 (in millions): 2020 2019 2018 Compensation cost: RSUs $ 106 $ 98 $ 98 Restricted stock — 1 2 Stock options 2 1 1 Total $ 108 $ 100 $ 101 The table below summarizes UAL's unearned compensation and weighted-average remaining period to recognize costs for all outstanding share-based awards that are probable of being achieved as of December 31, 2020 (in millions, except as noted): Unearned Compensation Weighted-Average RSUs $ 80 1.5 Stock options 8 4.6 Total $ 88 RSUs. As of December 31, 2020, UAL had recorded a liability of approximately $29 million related to its cash-settled RSUs. UAL paid approximately $26 million, $41 million and $28 million related to its cash-settled RSUs during 2020, 2019 and 2018, respectively. The table below summarizes UAL's RSUs and restricted stock activity for the years ended December 31 (shares in millions): Liability Awards Equity Awards RSUs Weighted- Restricted Weighted- Outstanding at December 31, 2017 1.8 1.4 $ 63.99 0.3 $ 52.30 Granted 0.7 1.1 67.74 — — Vested (0.5) (0.5) 63.02 (0.2) 53.24 Forfeited (0.1) (0.2) 67.34 — — Outstanding at December 31, 2018 1.9 1.8 66.29 0.1 51.17 Granted 0.1 1.1 86.72 — — Vested (0.5) (0.8) 64.85 (0.1) 51.17 Forfeited (0.9) (0.1) 76.48 — — Outstanding at December 31, 2019 0.6 2.0 78.03 — — Granted 0.1 2.4 40.80 — — Vested (0.3) (0.8) 74.54 — — Forfeited — (0.4) 54.21 — — Outstanding at December 31, 2020 0.4 3.2 53.41 — — The fair value of RSUs and restricted stock that vested in 2020, 2019 and 2018 was $87 million, $99 million and $70 million, respectively. The fair value of the restricted stock and the stock-settled RSUs was based upon the UAL common stock price on the date of grant. The fair value of the cash-settled RSUs was based on the UAL common stock price as of the last day preceding the settlement date. Stock Options. UAL did not grant any stock option awards during either 2020 or 2018. In 2019, UAL granted an award of approximately 307,000 premium-priced stock options with an exercise price that was 25% higher than the closing price of UAL's common stock on the date of grant, representing an exercise price of $110.21. Expense related to each portion of an option grant is recognized on a straight-line basis over the specific vesting period for those options. As of December 31, 2020, there were approximately 0.7 million outstanding stock option awards, 0.3 million of which were exercisable, with weighted-average exercise prices of $82.12 and $58.25, respectively, weighted-average remaining contractual lives (in years) of 6.3 and 3.5, respectively, and intrinsic values of zero as all of the exercise prices exceeded the closing stock price on that date.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Accumulated Other Comprehensive Income (Loss)	ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) ("AOCI") The tables below present the components of the Company's AOCI, net of tax (in millions): Pension and Investments and Other Deferred Taxes Total Balance at December 31, 2017 $ (1,102) $ (6) $ (39) $ (1,147) Change in value 377 (5) (83) 289 Amounts reclassified to earnings 62 (a) — (13) 49 Amounts reclassified to retained earnings ("RE") — 7 (b) (1) (b) 6 Balance at December 31, 2018 (663) (4) (136) (803) Change in value 105 7 (24) 88 Amounts reclassified to earnings (2) (a) (1) — (3) Balance at December 31, 2019 (560) 2 (160) (718) Change in value (993) — 221 (772) Amounts reclassified to earnings 451 (a) — (100) 351 Balance at December 31, 2020 $ (1,102) $ 2 $ (39) $ (1,139) (a) This AOCI component is included in the computation of net periodic pension and other postretirement costs. See Note 7 of this report for additional information on pensions and other postretirement liabilities. (b) These amounts represent the reclassification from AOCI to RE of the unrealized loss, and related tax, on the Company's investment in Azul Linhas Aéreas Brasileiras S.A. ("Azul") which was classified as an available-for-sale security prior to the Company adopting Accounting Standards Update No. 2016-01, Financial Instruments—Overall (Subtopic 825-10) effective January 1, 2018.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES The income tax provision (benefit) differed from amounts computed at the statutory federal income tax rate and consisted of the following significant components (in millions) : UAL 2020 2019 2018 Income tax provision (benefit) at statutory rate $ (1,852) $ 822 $ 556 State income taxes, net of federal income tax benefit (110) 50 29 Foreign tax rate differential — (90) (84) Global intangible low-taxed income — 90 4 Foreign income taxes 1 1 2 Nondeductible employee meals 5 12 12 State rate change (2) — 3 Valuation allowance 197 (4) (3) Other, net 8 24 7 $ (1,753) $ 905 $ 526 Current $ (12) $ 23 $ 14 Deferred (1,741) 882 512 $ (1,753) $ 905 $ 526 United 2020 2019 2018 Income tax provision (benefit) at statutory rate $ (1,852) $ 822 $ 557 State income taxes, net of federal income tax (110) 50 29 Foreign tax rate differential — (90) (84) Global intangible low-taxed income — 90 4 Foreign income taxes 1 1 2 Nondeductible employee meals 5 12 12 State rate change (2) — 3 Valuation allowance 197 (4) (3) Other, net 8 24 7 $ (1,753) $ 905 $ 527 Current $ (12) $ 23 $ 14 Deferred (1,741) 882 513 $ (1,753) $ 905 $ 527 The Company's effective tax rate for the year ended December 31, 2020 differed from the federal statutory rate of 21% due to a blend of federal, state and foreign taxes as well as the impact of certain nondeductible items and a valuation allowance of $197 million related to capital losses and state attributes. Temporary differences and carryforwards that give rise to deferred tax assets and liabilities at December 31, 2020 and 2019 were as follows (in millions): UAL United 2020 2019 2020 2019 Deferred income tax asset (liability): Federal and state net operating loss ("NOL") carryforwards $ 2,476 $ 695 $ 2,448 $ 668 Deferred revenue 1,409 1,287 1,409 1,287 Employee benefits, including pension, postretirement and medical 1,103 715 1,103 715 Operating lease liabilities 1,247 1,256 1,247 1,256 Sale leaseback liabilities 260 — 260 — Other 362 165 362 165 Less: Valuation allowance (247) (58) (247) (58) Total deferred tax assets $ 6,610 $ 4,060 $ 6,582 $ 4,033 Depreciation $ (4,789) $ (4,011) $ (4,789) $ (4,011) Operating lease right-of-use asset (1,028) (1,061) (1,028) (1,061) Intangibles (662) (724) (662) (724) Total deferred tax liabilities $ (6,479) $ (5,796) $ (6,479) $ (5,796) Net deferred tax asset (liability) $ 131 $ (1,736) $ 103 $ (1,763) United and its domestic consolidated subsidiaries file a consolidated federal income tax return with UAL. Under an intercompany tax allocation policy, United and its subsidiaries compute, record and pay UAL for their own tax liability as if they were separate companies filing separate returns. In determining their own tax liabilities, United and each of its subsidiaries take into account all tax credits or benefits generated and utilized as separate companies and they are each compensated for the aforementioned tax benefits only if they would be able to use those benefits on a separate company basis. The Company's federal and state NOL and tax credit carryforwards relate to current and prior years' NOLs and credits, which may be used to reduce tax liabilities in future years. These tax benefits are mostly attributable to federal pre-tax NOL carryforwards of $11.0 billion ($2.3 billion tax effected) for UAL. If not utilized these federal pre-tax NOLs will expire as follows (in billions): $0.1 in 2026, $0.5 in 2028, and $0.4 in 2029, $0.2 in 2032 and $0.4 in 2033. The remaining $9.4 billion of NOLs has no expiration date. State pre-tax NOLs of $3.7 billion ($0.2 billion tax effected) expire over a five twenty one one A tax valuation allowance is recognized if it is more likely than not that some portion or all of the deferred tax assets will not be realized. The Company's management assesses available positive and negative evidence regarding the Company's ability to realize its deferred tax assets and records a valuation allowance when it is more likely than not that deferred tax assets will not be realized. In order to form a conclusion, management considers positive evidence in the form of taxable income in prior carryback years, reversing temporary differences, tax planning strategies and projections of future taxable income during the periods in which those temporary differences become deductible, as well as negative evidence such as historical losses. Although the Company was in a cumulative loss position at the end of 2020, management determined that the 2020 results were not indicative of future results due to the impact of the COVID-19 pandemic on its operations. The Company concluded that the positive evidence outweighs the negative evidence, primarily driven by approval and distribution of COVID-19 vaccines as well as increased confidence with the timing of the recovery. The Company's largest deferred tax assets are mostly attributable to federal pre-tax NOLs which were $11.0 billion ($2.3 billion tax effected) at December 31, 2020. The majority of the NOLs do not expire and the Company expects to recognize the NOLs through the reversal of existing deferred tax liabilities and projected future taxable income. Therefore, we have not recorded a valuation allowance on our deferred tax assets other than the capital loss carryforwards and state attributes that have short expiration periods. While the Company expects to generate sufficient future profits to fully utilize these NOLs, the Company may have to record a valuation allowance against our NOLs if it is unable to generate sufficient taxable income in future periods. Recording a valuation allowance against our NOLs would not impact our ability to use them. Assumptions about future taxable income are consistent with the plans and estimates used to manage our business. Management will continue to evaluate future financial performance to determine whether such performance is both sustained and significant enough to provide sufficient evidence to support not recording valuation allowance on these NOLs. Any reduction in estimated future taxable income may require additional valuation allowance against the deferred tax assets, which could be material. As of December 31, 2020, the Company has recorded $185 million of valuation allowance against its capital loss deferred tax assets. Capital losses have a limited carryforward period of five years and they can be utilized only to the extent of capital gains. The Company does not anticipate generating sufficient capital gains to utilize the losses before they expire, therefore, a valuation allowance is necessary as of December 31, 2020. Additionally, the Company recorded a valuation allowance of $62 million on the state NOL and state tax credit deferred tax assets primarily due to utilization limitations resulting from a prior ownership change. The Company's unrecognized tax benefits related to uncertain tax positions were $57 million, $53 million and $39 million at December 31, 2020, 2019 and 2018, respectively. Included in the ending balance at December 31, 2020 is $57 million that would affect the Company's effective tax rate if recognized. The changes in unrecognized tax benefits relating to settlements with taxing authorities, unrecognized tax benefits as a result of tax positions taken during a prior period and unrecognized tax benefits relating from a lapse of the statute of limitations were immaterial during 2020, 2019 and 2018. The Company does not expect significant increases or decreases in their unrecognized tax benefits within the next 12 months. There are no material amounts included in the balance at December 31, 2020 for tax positions for which the ultimate deductibility is highly certain but for which there is uncertainty about the timing of such deductibility. The Company's federal income tax returns for tax years after 2002 remain subject to examination by the Internal Revenue Service (the "IRS") and state taxing jurisdictions. We are currently under audit by the IRS for the 2016 and 2017 tax years.

Pension and Other Postretiremen

Pension and Other Postretirement Plans	12 Months Ended
	Dec. 31, 2020
Retirement Benefits [Abstract]
Pension and Other Postretirement Plans	PENSION AND OTHER POSTRETIREMENT PLANS The following summarizes the significant pension and other postretirement plans of United: Pension Plans. United maintains two primary defined benefit pension plans, one covering certain pilot employees and another covering certain U.S. non-pilot employees. Each of these plans provide benefits based on a combination of years of benefit accruals service and an employee's final average compensation. Additional benefit accruals are frozen under the plan covering certain pilot employees and for management and administrative employees covered under the non-pilot plan. Benefit accruals for certain non-pilot employees continue. United maintains additional defined benefit pension plans, which cover certain international employees. Other Postretirement Plans. United maintains postretirement medical programs which provide medical benefits to certain retirees and eligible dependents, as well as life insurance benefits to certain retirees participating in the plan. Benefits provided are subject to applicable contributions, co-payments, deductibles and other limits as described in the specific plan documentation. During 2020, the Company offered voluntary separation programs ("VSPs") to its U.S.-based front-line employees and management and administrative employees. The Company offered certain of its eligible front-line employees, based on employee group, age and completed years of service, special termination benefits in the form of additional years of pension service and additional subsidies for retiree medical costs. These benefits resulted in a $54 million special termination benefit charges for the pension plans and $201 million for the retiree medical plan. The VSPs and other separation programs caused the lump sum settlements to increase in 2020. In 2020, the primary defined benefit pension plans paid $1.4 billion in lump sum distributions resulting in the recognition of $430 million of settlement losses. Settlement losses trigger the recognition of losses previously reported as unrealized in accumulated other comprehensive loss in an amount that is proportionate to the lump sum distributions as a percentage of the obligations of the plan. Actuarial assumption changes are reflected as a component of the net actuarial (gain) loss during 2020 and 2019. The 2020 actuarial losses were mainly related to a decrease in the discount rate applied at December 31, 2020 compared to December 31, 2019. Actuarial (gains) losses will be amortized over the average remaining service life of the covered active employees or the average life expectancy of inactive participants. The following tables set forth the reconciliation of the beginning and ending balances of the benefit obligation and plan assets, the funded status and the amounts recognized in these financial statements for the defined benefit and other postretirement plans (in millions): Pension Benefits Year Ended December 31, 2020 Year Ended December 31, 2019 Accumulated benefit obligation: $ 5,387 $ 5,333 Change in projected benefit obligation: Projected benefit obligation at beginning of year $ 6,398 $ 5,396 Service cost 216 184 Interest cost 209 226 Actuarial loss 1,181 784 Special termination benefit 54 — Benefits paid (1,445) (200) Curtailment (105) — Other 17 8 Projected benefit obligation at end of year $ 6,525 $ 6,398 Change in plan assets: Fair value of plan assets at beginning of year $ 4,964 $ 3,827 Actual return on plan assets 521 684 Employer contributions 16 649 Benefits paid (1,445) (200) Other 13 4 Fair value of plan assets at end of year $ 4,069 $ 4,964 Funded status—Net amount recognized $ (2,456) $ (1,434) Pension Benefits December 31, 2020 December 31, 2019 Amounts recognized in the consolidated balance sheets consist of: Noncurrent asset $ 8 $ 14 Current liability (4) (2) Noncurrent liability (2,460) (1,446) Total liability $ (2,456) $ (1,434) Amounts recognized in accumulated other comprehensive loss consist of: Net actuarial loss $ (1,924) $ (1,652) Prior service cost (3) (4) Total accumulated other comprehensive loss $ (1,927) $ (1,656) Other Postretirement Benefits Year Ended December 31, 2020 Year Ended December 31, 2019 Change in benefit obligation: Benefit obligation at beginning of year $ 842 $ 1,391 Service cost 10 10 Interest cost 28 47 Plan participants' contributions 58 67 Benefits paid (164) (180) Actuarial loss 107 99 Plan amendments — (597) Special termination benefit 201 — Other — 5 Benefit obligation at end of year $ 1,082 $ 842 Change in plan assets: Fair value of plan assets at beginning of year $ 52 $ 53 Actual return on plan assets 1 1 Employer contributions 104 111 Plan participants' contributions 58 67 Benefits paid (164) (180) Fair value of plan assets at end of year 51 52 Funded status—Net amount recognized $ (1,031) $ (790) Other Postretirement Benefits December 31, 2020 December 31, 2019 Amounts recognized in the consolidated balance sheets consist of: Current liability $ (37) $ (1) Noncurrent liability (994) (789) Total liability $ (1,031) $ (790) Amounts recognized in accumulated other comprehensive income consist of: Net actuarial gain $ 255 $ 403 Prior service credit 570 693 Total accumulated other comprehensive income $ 825 $ 1,096 The following information relates to all pension plans with an accumulated benefit obligation and a projected benefit obligation in excess of plan assets at December 31 (in millions): 2020 2019 Projected benefit obligation $ 6,250 $ 6,161 Accumulated benefit obligation 5,163 5,137 Fair value of plan assets 3,786 4,714 Net periodic benefit cost for the years ended December 31 included the following components (in millions): 2020 2019 2018 Pension Benefits Other Postretirement Benefits Pension Benefits Other Postretirement Benefits Pension Benefits Other Postretirement Benefits Service cost $ 216 $ 10 $ 184 $ 10 $ 228 $ 12 Interest cost 209 28 226 47 217 61 Expected return on plan assets (328) (1) (291) (1) (292) (2) Amortization of unrecognized actuarial (gain) loss 162 (40) 118 (52) 130 (32) Amortization of prior service credits — (124) — (73) — (37) Settlement loss - VSPs 430 — — — — — Special termination benefit - VSPs 54 201 — — — — Curtailment 1 — — — — — Other 22 — 5 — 1 — Net periodic benefit cost (credit) $ 766 $ 74 $ 242 $ (69) $ 284 $ 2 Service cost is recorded in Salaries and related costs on the statement of consolidated operations. All other components of net periodic benefit costs are recorded in Miscellaneous, net on the statement of consolidated operations. The assumptions used for the benefit plans were as follows: Pension Benefits Assumptions used to determine benefit obligations 2020 2019 Discount rate 2.72 % 3.52 % Rate of compensation increase 3.88 % 3.89 % Assumptions used to determine net expense Discount rate 3.51 % 4.21 % Expected return on plan assets 7.31 % 7.40 % Rate of compensation increase 3.88 % 3.89 % A 50 basis points decrease in the weighted average discount rate would have increased the Company's December 31, 2020 pension benefit liability by approximately $0.8 billion and increased the estimated 2020 pension benefit expense by approximately $78 million. Other Postretirement Benefits Assumptions used to determine benefit obligations 2020 2019 Discount rate 2.43 % 3.35 % Assumptions used to determine net expense Discount rate 3.35 % 4.30 % Expected return on plan assets 3.00 % 3.00 % Health care cost trend rate assumed for next year 5.80 % 6.00 % Rate to which the cost trend rate is assumed to decline (ultimate trend rate in 2033) 4.50 % 5.00 % A 50 basis points decrease in the weighted average discount rate would have increased the Company's December 31, 2020 postretirement benefit liability by approximately $48 million and increased the estimated 2020 benefits expense by approximately $2 million. The Company used the Society of Actuaries' PRI-2012 Private Retirement Plans Mortality Tables projected generationally using the Society of Actuaries' MP-2020 projection scale. The Company selected the 2020 discount rate for substantially all of its plans by using a hypothetical portfolio of high-quality bonds at December 31, 2020, that would provide the necessary cash flows to match projected benefit payments. We develop our expected long-term rate of return assumption for our defined benefit plans based on historical experience and by evaluating input from the trustee managing the plans' assets. Our expected long-term rate of return on plan assets for these plans is based on a target allocation of assets, which is based on our goal of earning the highest rate of return while maintaining risk at acceptable levels. The plans strive to have assets sufficiently diversified so that adverse or unexpected results from one security class will not have an unduly detrimental impact on the entire portfolio. Plan fiduciaries regularly review our actual asset allocation and the pension plans' investments are periodically rebalanced to our targeted allocation when considered appropriate. United's plan assets are allocated within the following guidelines: Percent of Total Expected Long-Term Equity securities 30-45 % 10 % Fixed-income securities 35-50 4 Alternatives 15-25 7 A 50 basis points decrease in the expected long-term rate of return on plan assets would have increased estimated 2020 pension expense by approximately $25 million. Fair Value Information. Accounting standards require us to use valuation techniques to measure fair value that maximize the use of observable inputs and minimize the use of unobservable inputs. These inputs are prioritized as follows: Level 1 Unadjusted quoted prices in active markets for assets or liabilities identical to those to be reported at fair value Level 2 Other inputs that are observable directly or indirectly, such as quoted prices for similar assets or liabilities or market-corroborated inputs Level 3 Unobservable inputs for which there is little or no market data and which require us to develop our own assumptions about how market participants would price the assets or liabilities Assets and liabilities measured at fair value are based on the valuation techniques identified in the tables below. The valuation techniques are as follows: (a) Market approach. Prices and other relevant information generated by market transactions involving identical or comparable assets and liabilities; and (b) Income approach. Techniques to convert future amounts to a single current value based on market expectations (including present value techniques, option-pricing and excess earnings models). The following tables present information about United's pension and other postretirement plan assets at December 31 (in millions): 2020 2019 Pension Plan Assets: Total Level 1 Level 2 Level 3 Assets Measured at NAV(a) Total Level 1 Level 2 Level 3 Assets Measured at NAV(a) Equity securities funds $ 1,606 $ 55 $ 125 $ 96 $ 1,330 $ 1,957 $ 47 $ 117 $ 71 $ 1,722 Fixed-income securities 1,644 — 548 49 1,047 1,732 — 687 69 976 Alternatives 669 — — 195 474 776 — — 205 571 Other investments 150 132 8 10 — 499 466 21 12 — Total $ 4,069 $ 187 $ 681 $ 350 $ 2,851 $ 4,964 $ 513 $ 825 $ 357 $ 3,269 Other Postretirement Benefit Plan Assets: Deposit administration fund $ 51 $ — $ — $ 51 $ — $ 52 $ — $ — $ 52 $ — (a) In accordance with the relevant accounting standards, certain investments that are measured at fair value using the net asset value ("NAV") per share (or its equivalent) have not been classified in the fair value hierarchy. These investments are commingled funds that invest in fixed-income instruments including bonds, debt securities, and other similar instruments issued by various U.S. and non-U.S. public- or private-sector entities. Redemption periods for these investments range from daily to semiannually. Equity and Fixed-Income. Equities include investments in both developed market and emerging market equity securities. Fixed-income includes primarily U.S. and non-U.S. government fixed-income securities and U.S. and non-U.S. corporate fixed-income securities. Deposit Administration Fund. This investment is a stable value investment product structured to provide investment income. Alternatives. Alternative investments consist primarily of investments in hedge funds, real estate and private equity interests. Other investments. Other investments consist of primarily cash, as well as insurance contracts. The reconciliation of United's benefit plan assets measured at fair value using unobservable inputs (Level 3) for the years ended December 31, 2020 and 2019 is as follows (in millions): 2020 2019 Balance at beginning of year $ 409 $ 350 Actual return (loss) on plan assets: Sold during the year 4 12 Held at year end 13 (1) Purchases, sales, issuances and settlements (net) (25) 48 Balance at end of year $ 401 $ 409 Funding requirements for tax-qualified defined benefit pension plans are determined by government regulations. The Company did not have any minimum required contributions for 2020 and does not expect any for 2021. The Company expects to make approximately $82 million in contributions to United's postretirement plans in 2021. The estimated future benefit payments, net of expected participant contributions, in United's pension plans and other postretirement benefit plans as of December 31, 2020 are as follows (in millions): Pension Other Postretirement 2021 $ 325 $ 88 2022 339 118 2023 353 100 2024 351 87 2025 376 83 Years 2026 – 2030 2,113 359 Defined Contribution Plans. United offers several defined contribution plans to its employees. Depending upon the employee group, employer contributions consist of matching contributions and/or non-elective employer contributions. United's employer contribution percentages to its primary 401(k) defined contribution plans vary from 1% to 16% of eligible earnings depending on the terms of each plan. United recorded expenses for its primary 401(k) defined contribution plans of $687 million, $735 million and $693 million in the years ended December 31, 2020, 2019 and 2018, respectively. Multi-Employer Plans. United's participation in the IAM National Pension Plan ("IAM Plan") for the annual period ended December 31, 2020 is outlined in the table below. In addition to the additional required contributions described in table below, contributions in 2020 were affected by COVID-19 impacts on United's operations and consequently employee hours paid. The risks of participating in these multi-employer plans are different from single-employer plans, as United may be subject to additional risks that others do not meet their obligations, which in certain circumstances could revert to United. The IAM Plan reported $510 million in employers' contributions for the year ended December 31, 2019. For 2019, the Company's contributions to the IAM Plan represented more than 10% of total contributions to the IAM Plan. The 2020 information is not available as Form 5500 is not final for the plan year. Pension Fund IAM National Pension Fund ("Fund") EIN/ Pension Plan Number 51-6031295 — 002 Pension Protection Act Zone Status (2020 and 2019) Critical (2020) and Endangered (2019). A plan generally is in "endangered" status if its funded percentage is less than 80 percent. A plan is in "critical" status if the funded percentage is less than 65 percent. On April 17, 2019, the IAM National Pension Fund Board of Trustees voluntarily elected for the Fund to be in critical status effective for the plan year beginning January 1, 2019 to strengthen the Fund's financial health. FIP/RP Status Pending/Implemented A 10-year Rehabilitation Plan effective, January 1, 2022, was adopted on April 17, 2019 that requires the Company to make an additional contribution of 2.5% of the hourly contribution rate, compounded annually for the length of the Rehabilitation Plan, effective June 1, 2019. United's Contributions $53 million, $59 million and $52 million in the years ended December 31, 2020, 2019 and 2018, respectively Surcharge Imposed No Expiration Date of Collective Bargaining Agreement N/A Profit Sharing. Substantially all employees participate in profit sharing based on a percentage of pre-tax earnings, excluding special charges, profit sharing expense and share-based compensation. Profit sharing percentages range from 5% to 20% depending on the work group, and in some cases profit sharing percentages vary above and below certain pre-tax margin thresholds. Eligible U.S. co-workers in each participating work group receive a profit sharing payout using a formula based on the ratio of each qualified co-worker's annual eligible earnings to the eligible earnings of all qualified co-workers in all domestic work groups. Eligible non-U.S. co-workers receive profit sharing based on the calculation under the U.S. profit sharing plan for management and administrative employees. As a result of the pre-tax losses in 2020, no profit sharing was recorded. However, the Company recorded profit sharing and related payroll tax expense of $491 million and $334 million in 2019 and 2018, respectively. Profit sharing expense is recorded as a component of Salaries and related costs in the Company's statements of consolidated operations.

Notes Receivable

Notes Receivable	12 Months Ended
	Dec. 31, 2020
Receivables [Abstract]
Notes Receivables	NOTES RECEIVABLE BRW Term Loan. In November 2018, United, as lender, entered into a Term Loan Agreement (the "BRW Term Loan Agreement") with, among others, BRW Aviation Holding LLC and BRW Aviation LLC ("BRW"), as guarantor and borrower, respectively. BRW Aviation Holding LLC and BRW are affiliates of Synergy Aerospace Corporation ("Synergy"), and BRW is the majority shareholder of Avianca Holdings S.A. ("AVH"). Pursuant to the BRW Term Loan Agreement, United provided to BRW a $456 million term loan (the "BRW Term Loan"), secured by a pledge of BRW's equity, as well as BRW's 516 million common shares of AVH (which are eligible to be converted into the same number of preferred shares, which may be deposited with the depositary for AVH's American Depositary Receipts ("ADRs"), the class of AVH securities that trades on the New York Stock Exchange (the "NYSE"), in exchange for 64.5 million ADRs) (such shares and equity, collectively, the "BRW Loan Collateral"). In the first quarter of 2020, United recorded a full credit loss allowance against the $515 million carrying value of the BRW Term Loan and related receivables. United recorded the allowance based on United's assessment of AVH's financial uncertainty due to its high level of leverage and the fact that the airline had ceased operations due to the COVID-19 pandemic. The credit loss allowance was recorded as part of Nonoperating income (expense): Miscellaneous, net on the Company's statements of consolidated operations. AVH and certain of its affiliates filed voluntary reorganization proceedings under Chapter 11 of the United States Bankruptcy Code in the U.S. Bankruptcy Court for the Southern District of New York on May 10, 2020 (the "AVH Reorganization Proceedings"). Accordingly, United maintains a full loss reserve against the BRW Term Loan and related receivables. In connection with funding the BRW Term Loan Agreement, the Company entered into certain other agreements with Kingsland. See Note 13 of this report for additional information regarding our obligations to Kingsland and their interrelationship with the BRW Term Loan Agreement. Avianca Loan. In November 2019, United entered into a senior secured convertible term loan agreement (the "AVH Convertible Loan Agreement") with, among others, AVH, as borrower, for the provision by the lenders thereunder (including United) to AVH of convertible term loans for general corporate purposes. In December 2019, United provided such a Other. The Company has

Investments and Fair Value Meas

Investments and Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Investments and Fair Value Measurements	INVESTMENTS AND FAIR VALUE MEASUREMENTS Fair Value Information. Accounting standards require us to use valuation techniques to measure fair value that maximize the use of observable inputs and minimize the use of unobservable inputs. These inputs are described in Note 7 of this report. The table below presents disclosures about the fair value of financial assets and liabilities measured at fair value on a recurring basis in the Company's financial statements as of December 31 (in millions): 2020 2019 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Cash and cash equivalents $ 11,269 $ 11,269 $ — $ — $ 2,762 $ 2,762 $ — $ — Restricted cash - current (Note 1) 255 255 — — — — — — Restricted cash - non-current (Note 1) 218 218 — — 106 106 — — Short-term investments: Corporate debt 330 — 330 — 1,045 — 1,045 — Asset-backed securities 51 — 51 — 690 — 690 — U.S. government and agency notes 33 — 33 — 124 — 124 — Certificates of deposit placed through an account registry service — — — — 35 — 35 — Other fixed-income securities — — — — 95 — 95 — Other investments measured at NAV — — — — 193 — — — Long-term investments: Equity securities 205 205 — — 385 385 — — AVH Derivative Assets — — — — 24 — — 24 Other assets 36 — — 36 — — — — Short-term investments - T he short-term investments shown in the table above are classified as available-for-sale, with the exception of investments measured at NAV. As of December 31, 2020, corporate debt securities have remaining maturities of approximately two years or less, asset-backed securities have remaining maturities of less than one year to approximately 14 years, and U.S. government and agency notes have maturities of less than one year. Equity securities - Equity securities represent United's investment in Azul, consisting of approximately 8% of Azul's outstanding preferred shares (representing approximately 2% of the total capital stock of Azul). The Company recorded $180 million in losses and $136 million in gains, respectively, for the years ended December 31, 2020 and 2019 for changes to the fair market value of its equity investment in Azul in Unrealized gains (losses) on investments, net in the Company's statements of consolidated operations. The carrying value of our investment in Azul was $205 million at December 31, 2020. AVH Derivative Assets - As part of the BRW Term Loan Agreement and related agreements with Kingsland, United obtained AVH share call options and AVH share appreciation rights and entered into an AVH share-based upside sharing agreement (collectively, the "AVH Derivative Assets"). The AVH Derivative Assets are recorded at fair value as Other assets on the Company's balance sheet and are included in the table above. The Company recorded $24 million in losses and $13 million in gains, respectively, for the years ended December 31, 2020 and 2019 for changes in the fair value of the AVH Derivative Assets in Unrealized gains (losses) on investments, net in the Company's statements of consolidated operations. Other assets - The other assets represent warrants provided to United for the purchase of membership units (Class B Units) in Alclear Holdings, LLC ("CLEAR"). The Company records these warrants at fair value. Investments presented in the table above have the same fair value as their carrying value. Other fair value information - The table below presents the carrying values and estimated fair values of financial instruments not presented in the tables above as of December 31 (in millions). Carrying amounts include any related discounts, premiums and issuance costs: 2020 2019 Carrying Amount Fair Value Carrying Amount Fair Value Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Long-term debt $ 26,747 $ 27,441 $ — $ 21,985 $ 5,456 $ 14,552 $ 15,203 $ — $ 11,398 $ 3,805 Fair value of the financial instruments included in the tables above was determined as follows: Description Fair Value Methodology Cash and cash equivalents The carrying amounts approximate fair value because of the short-term maturity of these assets. Short-term investments, other than Other investments measured at NAV, Fair value is based on (a) the trading prices of the investment or similar instruments, (b) an income approach, which uses valuation techniques to convert future amounts into a single present amount based on current market expectations about those future amounts when observable trading prices are not available, or (c) broker quotes obtained by third-party valuation services. Other investments measured at NAV In accordance with the relevant accounting standards, certain investments that are measured at fair value using the NAV per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in the table above are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the statement of financial position. The investments measured using NAV are shares of mutual funds that invest in fixed-income instruments including bonds, debt securities, and other similar instruments issued by various U.S. and non-U.S. public- or private-sector entities. The Company can redeem its shares at any time at NAV subject to a three-day settlement period. AVH Derivative Assets Fair values are calculated using a Monte Carlo simulation approach. Unobservable inputs include expected volatility, expected dividend yield and control and acquisition premiums. Other assets Fair value is determined utilizing the Black-Scholes options pricing model. Long-term debt Fair values were based on either market prices or the discounted amount of future cash flows using our current incremental rate of borrowing for similar liabilities or assets. Investments in Regional Carriers . United holds investments in several regional carriers that fly for the Company as United Express under its CPAs. The combined carrying value of the investments was approximately $139 million as of December 31, 2020. United accounts for each investment using the equity method. Each investment and United's ownership stake are listed below. • Republic Airways Holdings Inc. ("Republic"). United holds a 19% minority interest in Republic. Republic is the parent company of Republic Airways Inc. Republic currently operates 66 regional aircraft under a CPA that has terms through 2029. • ManaAir, LLC ("ManaAir"). United holds a 49.9% minority ownership stake in ManaAir. ManaAir is the parent company of ExpressJet Airlines LLC ("ExpressJet"). The Company terminated its CPA with ExpressJet. ExpressJet flew its last commercial flight, on behalf of United, on September 30, 2020. • Champlain Enterprises, LLC ("Champlain"). United owns a 40% minority ownership stake in Champlain. Champlain does business as CommutAir ("CommutAir"). As of December 31, 2020, CommutAir operated 49 regional aircraft and is expected to operate additional ERJ 145 regional jets that were formerly part of the ExpressJet fleet. Other Investments. United holds other investments that are recorded at cost less impairment, adjusted for observable price changes in orderly transactions for an identical or similar investment of the same issuer. As of December 31, 2020, United held these major investments: • Fulcrum BioEnergy, Inc. ("Fulcrum"). United owns approximately 7% of the preferred shares (representing approximately 6% of the total capital stock) of Fulcrum, a company that is developing a process for transforming municipal solid waste into transportation fuels, including jet fuel and diesel. As of December 31, 2020, the carrying value of United's investment was $51 million. • CLEAR. United owns less than 1% of the Class B Units of CLEAR, a technology-enabled experience company that owns and operates a secure identity platform. Using biometrics, CLEAR enables touchless identification at airport checkpoints and other venues. As of December 31, 2020, the carrying value of United's investment was approximately $9 million.

Debt

Debt	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Debt	DEBT (In millions) Maturity Dates Interest Rate(s) at December 31, 2020 At December 31, 2020 2019 Secured Aircraft notes (a) 2021 — 2032 0.73 % — 9.80 % $ 14,538 $ 11,585 MileagePlus Senior Secured Notes 2027 6.50 % 3,800 — MileagePlus Term Loan Facility (a) 2027 5.49 % 3,000 — Revolving Credit Facility (a) 2022 1.49 % 1,000 — CARES Act Term Loan Facility (a) 2025 3.24 % 520 — Term Loan Facility (a) 2024 2.49 % 1,444 1,459 Unsecured Notes 2022 — 2025 4.25 % — 5.00 % 1,050 1,350 PSP Note 2030 1.00 % 1,501 — Other unsecured debt 2023 — 2029 4.00 % — 5.75 % 448 339 27,301 14,733 Less: unamortized debt discount, premiums and debt issuance costs (554) (181) Less: current portion of long-term debt (1,911) (1,407) Long-term debt, net $ 24,836 $ 13,145 (a) Financing includes variable rate debt based on LIBOR (or another index rate), generally subject to a floor, plus a specified margin ranging from 0.49% to 5.25%. The table below presents the Company's contractual principal payments (not including debt discount or debt issuance costs) at December 31, 2020 under then-outstanding long-term debt agreements in each of the next five calendar years (in millions): 2021 $ 1,911 2022 3,852 2023 2,699 2024 5,132 2025 3,739 After 2025 9,968 $ 27,301 PSP Note. During 2020, pursuant to the PSP Agreement and in connection with Treasury providing the Company with total funding of approximately $5.1 billion under the Payroll Support Program of the CARES Act, UAL issued a promissory note to Treasury evidencing senior unsecured indebtedness of UAL of approximately $1.5 billion. The PSP Note is guaranteed by United and will mature on April 20, 2030, ten years after the initial issuance. If any subsidiary of UAL (other than United) guarantees other unsecured indebtedness of UAL with a principal balance in excess of a specified amount, or if certain subsidiaries are formed or acquired , then such subsidiary shall be required to guarantee the obligations of UAL under the PSP Note. UAL may, at its option, prepay the PSP Note, at any time, and from time to time, at par. UAL is required to prepay the PSP Note upon the occurrence of certain change of control triggering events. The PSP Note does not require any amortization and is to be repaid in full on the maturity date. Interest on the PSP Note is payable semi-annually in arrears on the last business day of March and September of each year beginning on September 30, 2020 at a rate of 1.00% in years one through five, and at the Secured Overnight Financing Rate (SOFR) plus 2.00% in years six through ten. MileagePlus Financing. On July 2, 2020, MPH and Mileage Plus Intellectual Property Assets, Ltd., an indirect wholly-owned subsidiary of MPH ("MIPA" and, together with MPH, the "Issuers") issued $3.8 billion aggregate principal amount of their 6.50% Senior Secured Notes due 2027 (the "Notes"). The Notes have a fixed annual interest rate of 6.50%, which will be paid in cash, quarterly in arrears on March 20, June 20, September 20 and December 20 of each year, beginning on September 21, 2020 (each a "Payment Date"). Concurrently with the issuance of the Notes, the Issuers entered into a credit agreement that provides for a term loan facility in an aggregate principal amount of up to $3.0 billion (the "MP Term Loan Facility"). On July 2, 2020, the Issuers borrowed $3.0 billion in aggregate principal amount under the MP Term Loan Facility. Loans outstanding under the MP Term Loan Facility will bear interest at a variable rate equal to LIBOR (but not less than 1.00% per annum), plus a margin of 5.25% per annum, payable on each Payment Date. The principal on the Notes and the MP Term Loan Facility will be repaid in quarterly installments on each Payment Date, beginning on September 20, 2022. The scheduled maturity date of the Notes and of the MP Term Loan Facility is June 20, 2027. The Issuers lent the proceeds of the Notes and of the MP Term Loan Facility to United, after depositing a portion of such proceeds in reserve accounts to cover future interest payments. The Notes and the loans under the MP Term Loan Facility are guaranteed by UAL, United and certain other subsidiaries of UAL. The Notes and the loans under the MP Term Loan Facility are secured by first-priority security interests in substantially all of the assets of the Issuers, other than excluded property and subject to certain permitted liens, including specified cash accounts that include the accounts into which MileagePlus revenues are or will be paid by United's marketing partners and by United. CARES Act Credit Agreement. On September 28, 2020, the Company entered into a Loan and Guarantee Agreement (the "CARES Act Credit Agreement"), among United, as borrower, UAL, as parent and guarantor, the subsidiaries of UAL other than United party thereto from time to time, as guarantors, Treasury, as lender, and The Bank of New York Mellon, as administrative and collateral agent. The CARES Act Credit Agreement provides for a CARES Act Term Loan Facility of up to approximately $7.5 billion pursuant to the Loan Program established under Section 4003(b)(1) of the CARES Act. The loans under the CARES Act Term Loan Facility may be disbursed in up to three disbursements on or before May 28, 2021. On September 28, 2020, United borrowed an amount equal to $520 million under the CARES Act Term Loan Facility. The principal amount must be repaid in a single installment on the maturity date on September 26, 2025. United may prepay all or a portion of the CARES Act Term Loan Facility from time to time, at par plus accrued and unpaid interest on the amount prepaid. Borrowings under the CARES Act Credit Agreement bear interest at a variable rate equal to LIBOR (but not less than 0%), plus a margin of 3.00% per annum. The obligations of United under the CARES Act Credit Agreement are secured by liens (i) on certain route authorities of United and certain related slots and gate leaseholds and other related assets, (ii) certain aircraft and (iii) certain flight simulators and related assets. Revolving Credit Facility. As of December 31, 2020, United had $1.0 billion available under the revolving credit facility of the Credit Agreement. The Credit Agreement provides for a term loan facility (the "Term Loan Facility") and a revolving credit facility (the "Revolving Credit Facility"). To maximize United's flexibility under a debt incurrence covenant contained in two of United's financings, on July 2, 2020, United took the proactive step of borrowing $1.0 billion under the Revolving Credit Facility, which leaves $1.0 billion available for borrowing under such agreement by United at any time until April 1, 2022. Borrowings under the Revolving Credit Facility bear interest at a variable rate equal to LIBOR (but not less than 0% per annum), plus a margin of 2.25% per annum, or (at United's election) another rate based on certain market interest rates, plus a margin of 1.25% per annum. United pays a commitment fee equal to 0.75% per annum on the undrawn amount available under the Revolving Credit Facility. Used Aircraft Bridge Loan. On March 9, 2020, the Company entered into a Term Loan Credit and Guaranty Agreement (the "Used Aircraft Credit Agreement"), among United, as borrower, UAL, as parent and guarantor, the subsidiaries of UAL other than United party thereto from time to time, as guarantors, the lenders party thereto from time to time and JP Morgan Chase Bank N.A., as administrative agent. United borrowed the full amount of $2 billion under the Used Aircraft Credit Agreement (the "Used Aircraft Facility"). The obligations of United under the Used Aircraft Bridge Loan were secured by liens on certain aircraft of United. The principal amount of the Used Aircraft Facility plus accrued interest was paid in full on October 28, 2020. Spare Parts Bridge Loan. On March 20, 2020, the Company entered into a Term Loan Credit and Guaranty Agreement (the "Spare Parts Credit Agreement"), among United, as borrower, UAL, as parent and guarantor, the subsidiaries of UAL other than United party thereto from time to time, as guarantors, the lenders party thereto from time to time and Goldman Sachs Bank USA, as administrative agent. United borrowed the full amount of $500 million under the Spare Parts Credit Agreement (the "Spare Parts Bridge Loan"). The obligations of United under the Spare Parts Bridge Loan were secured by liens on certain aircraft spare parts of United. The principal amount of the Spare Parts Bridge Loan plus accrued interest was paid in full on October 28, 2020. Spare Engines Bridge Loan. On April 7, 2020, the Company entered into a Term Loan Credit and Guaranty Agreement (the "Spare Engines Credit Agreement"), among United, as borrower, UAL, as parent and guarantor, the subsidiaries of UAL other than United party thereto from time to time, as guarantors, the lenders party thereto from time to time and Bank of America, N.A., as administrative agent. United borrowed the full amount of $250 million under the Spare Engines Credit Agreement (the "Spare Engines Bridge Loan"). The obligations of United under the Spare Engines Bridge Loan were secured by liens on certain aircraft spare engines of United. The principal amount of the Spare Engines Bridge Loan plus accrued interest was paid in full on October 28, 2020. SRG Bridge Loan. On June 30, 2020, the Company entered into a $200 million Term Loan Credit and Guaranty Agreement (the "SRG Bridge Loan"), among United, as borrower, UAL, as parent and guarantor, and Barclays Bank PLC, as administrative agent. The obligations of United under the SRG Bridge Loan were secured by liens on certain routes of United between cities in the U.S. and Europe, Israel, South America, and Mexico. United borrowed the full amount of the SRG Bridge Loan on July 1, 2020 and repaid it in full on September 29, 2020. Aircraft Notes. As of December 31, 2020, United had $12.1 billion principal amount of equipment notes outstanding issued under enhanced equipment trust certificates ("EETC") financings included in notes payable in the table of outstanding debt above. Generally, the structure of these EETC financings consists of pass-through trusts created by United to issue pass-through certificates, which represent fractional undivided interests in the respective pass-through trusts and are not obligations of United. The proceeds of the issuance of the pass-through certificates are used to purchase equipment notes which are issued by United and secured by aircraft and, in certain structures, spare engines and spare parts. United is responsible for the payment obligations under the equipment notes. In certain EETC structures, proceeds received from the sale of pass-through certificates are initially held by a depositary in escrow for the benefit of the certificate holders until United issues equipment notes to the trust, which purchases such notes with a portion of the escrowed funds. These escrowed funds are not guaranteed by United and are not reported as debt on United's consolidated balance sheet because the proceeds held by the depositary are not United's assets. In September 2019, October 2020 and February 2021, United created new EETC pass-through trusts, each of which issued pass-through certificates. The proceeds from the issuance of the pass-through certificates were used to purchase equipment notes issued by United and secured by aircraft and, in the case of the EETC entered into in October 2020, also by spare engines and spare parts. The Company records the debt obligation upon issuance of the equipment notes rather than upon the initial issuance of the pass-through certificates. Certain details of the pass-through trusts with proceeds received from issuance of debt in 2020 are as follows (in millions, except stated interest rate): EETC Class Principal Final expected distribution date Stated interest rate Total proceeds received from issuance of debt during 2020 Total debt recorded September 2019 AA $ 702 May 2032 2.70% $ 189 $ 702 September 2019 A 287 May 2028 2.90% 77 287 September 2019 B 232 May 2028 3.50% 62 232 October 2020 A 3,000 October 2027 5.88% 3,000 3,000 February 2021 B 600 January 2026 4.88% — — $ 4,821 $ 3,328 $ 4,221 In 2020, United borrowed approximately $691 million aggregate principal amount from various financial institutions to finance the purchase of several aircraft delivered in 2020. The notes evidencing these borrowings, which are secured by the related aircraft, mature in 2032 and have interest rates comprised of LIBOR plus a specified margin. In November 2019, at the request of United, the California Municipal Finance Authority issued its approximately $295 million special facility revenue bonds and loaned the proceeds of such bonds to United pursuant to a loan agreement to finance the costs of construction of an aircraft maintenance and ground service equipment complex at Los Angeles International Airport. The bonds bear interest at 4% per annum, payable semiannually, commencing July 15, 2020 through the July 15, 2029 maturity date. As security for United's obligations under the loan agreement, United also entered into a leasehold mortgage which grants to the trustee of the bonds (acting on behalf of the bondholders) a lien on United's interest in the leased premises and any improvements thereon owned by or leased to United. As of December 31, 2020, United had recorded approximately $159 million related to this debt. PSP2 Note. During the first quarter of 2021, UAL issued the PSP2 Note to Treasury evidencing senior unsecured indebtedness of UAL. The principal amount of the PSP2 Note will increase to 30% of any disbursement made by Treasury to United under the PSP2 Agreement after the initial issuance date to approximately $753 million aggregate principal amount after all disbursements. The PSP2 Note is guaranteed by United, and will mature ten years after issuance on January 15, 2031 (the "Maturity Date"). If any subsidiary of UAL (other than United) guarantees other unsecured indebtedness of UAL with a principal balance in excess of a specified amount, then such subsidiary shall be required to guarantee the obligations of UAL under the PSP2 Note. UAL may, at its option, prepay the PSP2 Note, at any time, and from time to time, at par. UAL is required to prepay the PSP2 Note upon the occurrence of certain change of control triggering events. The PSP2 Note does not require any amortization, and is to be repaid in full on the Maturity Date. Interest on the PSP2 Note is payable semi-annually in arrears on the last business day of March and September of each year, beginning on March 31, 2021, at a rate of 1.00% in years 1 through 5, and at the Secured Overnight Financing Rate (SOFR) plus 2.00% in years 6 through 10. As of December 31, 2020, UAL and United were in compliance with their respective debt covenants. The collateral, covenants and cross default provisions of the Company's principal debt instruments that contain such provisions are summarized in the table below: Debt Instrument Collateral, Covenants and Cross Default Provisions Various equipment notes and other notes payable Secured by certain aircraft, spare engines and spare parts. The indentures contain events of default that are customary for aircraft financings, including in certain cases cross default to other related aircraft. Credit Agreement Secured by certain of United's international route authorities, specified take-off and landing slots at certain airports and certain other assets. The Credit Agreement requires the Company to maintain at least $2.0 billion of unrestricted liquidity at all times, which includes unrestricted cash, short-term investments and any undrawn amounts under any revolving credit facility, and to maintain a minimum ratio of appraised value of collateral to the outstanding obligations under the Credit Agreement of 1.6 to 1.0 at all times. The Credit Agreement contains covenants that, among other things, restrict the ability of UAL and its restricted subsidiaries (as defined in the Credit Agreement) to make investments and to pay dividends on or repurchase stock. The Credit Agreement contains events of default customary for this type of financing, including a cross payment default and cross acceleration provision to certain other material indebtedness of the Company. CARES Act Credit Agreement Secured by liens on (i) certain route authorities of United and certain related slots and gate leaseholds and other related assets, (ii) certain aircraft and (iii) certain flight simulators and related assets. The CARES Act Credit Agreement requires the Company to maintain at least $2.0 billion of unrestricted liquidity at all times, which includes, among other things, unrestricted cash, certain short-term investments and any undrawn amounts under any revolving credit facility or under the CARES Act Credit Agreement, and to maintain a minimum ratio of appraised value of collateral to the outstanding obligations under the CARES Act Credit Agreement of 1.6 to 1.0. The CARES Act Credit Agreement contains covenants that, among other things, (i) restrict the ability of UAL and its subsidiaries to make investments and to pay dividends on or repurchase stock, (ii) require United to maintain certain levels of scheduled service and (iii) create certain limitations on executive compensation. The CARES Act Credit Agreement contains events of default customary for this type of financing, including a cross payment default and cross acceleration provision to certain other material indebtedness of the Company. MileagePlus Notes and Term Loan Facility Secured by first-priority security interests in substantially all of the assets of the Issuers, other than excluded property and subject to certain permitted liens, including security interests in specified cash accounts that include the accounts into which MileagePlus revenues are or will be paid by United's marketing partners and by United. PSP and PSP2 Notes The PSP Note and the PSP2 Note represent senior unsecured indebtedness of UAL. The PSP Note and the PSP2 Note are guaranteed by United. If any subsidiary of UAL (other than United) guarantees other unsecured indebtedness of UAL with a principal balance in excess of a specified amount, then such subsidiary shall be required to guarantee the obligations of UAL under the PSP Note and the PSP2 Note. Unsecured notes The indentures for these notes contain covenants that, among other things, restrict the ability of the Company and its restricted subsidiaries (as defined in the indentures) to incur additional indebtedness and pay dividends on or repurchase stock, although the Company currently has ample ability under these restrictions to repurchase stock under the Company's share repurchase programs.

Leases and Capacity Purchase Ag

Leases and Capacity Purchase Agreements	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases and Capacity Purchase Agreements	LEASES AND CAPACITY PURCHASE AGREEMENTSUnited leases aircraft, airport passenger terminal space, aircraft hangars and related maintenance facilities, cargo terminals, other airport facilities, other commercial real estate, office and computer equipment and vehicles, among other items. Certain of these leases include provisions for variable lease payments which are based on several factors, including, but not limited to, relative leased square footage, available seat miles, enplaned passengers, passenger facility charges, terminal equipment usage fees, departures, and airports' annual operating budgets. Due to the variable nature of the rates, these leases are not recorded on our balance sheet as a right-of-use asset and lease liability. For leases with terms greater than 12 months, we record the related right-of-use asset and lease liability at the present value of fixed lease payments over the lease term. To the extent a lease agreement includes an extension option that is reasonably certain to be exercised, we have recognized those amounts as part of our right-of-use assets and lease liabilities. Leases with an initial term of 12 months or less with purchase options or extension options that are not reasonably certain to be exercised are not recorded on the balance sheet; we recognize lease expense for these leases on a straight-line basis over the term of the lease. We combine lease and non-lease components, such as common area maintenance costs, in calculating the right-of-use assets and lease liabilities for all asset groups except for our CPAs, which contain embedded leases for regional aircraft. In addition to the lease component cost for regional aircraft, our CPAs also include non-lease components primarily related to the regional carriers' operating costs incurred in providing regional aircraft services. We allocate consideration for the lease components and non-lease components of each CPA based on their relative standalone values. Lease Cost . The Company's lease cost for the years ended December 31 included the following components (in millions): 2020 2019 2018 Operating lease cost $ 933 $ 1,038 $ 1,213 Variable and short-term lease cost 1,968 2,548 2,569 Amortization of finance lease assets 88 68 75 Interest on finance lease liabilities 16 85 44 Sublease income (23) (32) (38) Total lease cost $ 2,982 $ 3,707 $ 3,863 Lease terms and commitments . United's leases include aircraft leases for aircraft that are directly leased by United and aircraft that are operated by regional carriers on United's behalf under CPAs (but excluding aircraft owned by United) and non-aircraft leases. Aircraft operating leases relate to leases of 104 mainline and 290 regional aircraft while finance leases relate to leases of 37 mainline and 45 regional aircraft. United's aircraft leases have remaining lease terms of 1 month to 12 years with expiration dates ranging from 2021 through 2032. Under the terms of most aircraft leases, United has the right to purchase the aircraft at the end of the lease term, in some cases at fair market value, and in others, at a percentage of cost. Non-aircraft leases have remaining lease terms of 1 month to 32 years, with expiration dates ranging from 2021 through 2053. The table below summarizes the Company's scheduled future minimum lease payments under operating and finance leases, recorded on the balance sheet, as of December 31, 2020 (in millions): Operating Leases Finance Leases 2021 $ 847 $ 198 2022 693 59 2023 723 51 2024 704 47 2025 585 35 After 2025 3,979 64 Minimum lease payments 7,531 454 Imputed interest (1,933) (48) Present value of minimum lease payments 5,598 406 Less: current maturities of lease obligations (612) (182) Long-term lease obligations $ 4,986 $ 224 As of December 31, 2020, we have additional leases of approximately $740 million for several mainline aircraft, regional jets under a CPA and airport facilities and office space leases that have not yet commenced. These leases will commence in 2021 with lease terms of up to 12 years. In 2020, United entered into agreements with third parties to finance through sale and leaseback transactions new Boeing model 787-9 aircraft and Boeing model 737 MAX aircraft subject to purchase agreements between United and Boeing. In connection with the delivery of each aircraft from Boeing, United assigned its right to purchase such aircraft to the buyer, and simultaneous with the buyer's purchase from Boeing, United entered into a long-term lease for such aircraft with the buyer as lessor. Fifteen Boeing model aircraft were delivered in 2020 under these transactions (and each is presently subject to a long-term lease to United). Remaining aircraft in the agreements are scheduled to be delivered in 2021. Upon delivery of aircraft in these sale and leaseback transactions in 2020, the Company accounted for 11 of these aircraft, which have a repurchase option at a price other than fair value, as part of Flight equipment on the Company's balance sheet and the related obligation recorded in Other current liabilities and Other financial liabilities from sale-leasebacks (noncurrent) since they do not qualify for sale recognition. The remaining four aircraft that qualified for sale recognition were recorded as Operating lease right-of-use assets and Current/Long-term obligations under operating leases on the Company's balance sheet after recognition of related gains on such sale. See Note 14 of this report for additional information. Our lease agreements do not provide a readily determinable implicit rate nor is it available to us from our lessors. Instead, we estimate United's incremental borrowing rate based on information available at lease commencement in order to discount lease payments to present value. The table below presents additional information related to our leases as of December 31: 2020 2019 Weighted-average remaining lease term - operating leases 11 years 11 years Weighted-average remaining lease term - finance leases 4 years 6 years Weighted-average discount rate - operating leases 5.1 % 5.2 % Weighted-average discount rate - finance leases 4.4 % 5.7 % The table below presents supplemental cash flow information related to leases during the year ended December 31 (in millions): 2020 2019 2018 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows for operating leases $ 788 $ 902 $ 1,078 Operating cash flows for finance leases 20 70 53 Financing cash flows for finance leases 66 151 79 Regional CPAs. United has contractual relationships with various regional carriers to provide regional aircraft service branded as United Express. Under these CPAs, the Company pays the regional carriers contractually agreed fees (carrier costs) for operating these flights plus a variable rate adjustment based on agreed performance metrics, subject to annual adjustments. The fees are based on specific rates multiplied by specific operating statistics (e.g., block hours, departures), as well as fixed monthly amounts. Under these CPAs, the Company is also responsible for all fuel costs incurred, as well as landing fees and other costs, which are either passed through by the regional carrier to the Company without any markup or directly incurred by the Company. In some cases, the Company owns some or all of the aircraft subject to the CPA and leases such aircraft to the regional carrier. United's CPAs are for 475 regional aircraft as of December 31, 2020, and the CPAs have terms expiring through 2033. Aircraft operated under CPAs include aircraft leased directly from the regional carriers and those owned by United and operated by the regional carriers. See Part I, Item 2. Properties, of this report for additional information. In July 2020, the Company announced its plans to consolidate its Embraer ERJ 145 ("ERJ 145") operations into a single regional partner. As a result, the Company terminated its CPA with ExpressJet. ExpressJet flew its last commercial flight, on behalf of United, on September 30, 2020. Additionally, United transferred all of its ERJ 145 operations over to CommutAir as United's sole regional partner of this aircraft type. United recorded approximately $0.6 billion, $1.0 billion and $1.0 billion in expenses related to its CPAs with its regional carriers in which United is a minority shareholder, for the years ended December 31, 2020, 2019 and 2018, respectively. There were approximately $68 million and $69 million in accounts payable due to these companies as of December 31, 2020 and December 31, 2019, respectively. There were no material accounts receivables due from these companies as of December 31, 2020 and December 31, 2019. The CPAs with these related parties were executed in the ordinary course of business. Our future commitments under our CPAs are dependent on numerous variables, and are, therefore, difficult to predict. The most important of these variables is the number of scheduled block hours. Although we are not required to purchase a minimum number of block hours under certain of our CPAs, we have set forth below estimates of our future payments under the CPAs based on our assumptions. United's estimates of its future payments under all of the CPAs do not include the portion of the underlying obligation for any aircraft leased to a regional carrier or deemed to be leased from other regional carriers and facility rent that are disclosed as part of operating leases above. For purposes of calculating these estimates, we have assumed (1) the number of block hours flown is based on our anticipated level of flight activity or at any contractual minimum utilization levels if applicable, whichever is higher, (2) that we will reduce the fleet as rapidly as contractually allowed under each CPA, (3) that aircraft utilization, stage length and load factors will remain constant, (4) that each carrier's operational performance will remain at recent historic levels and (5) an annual projected inflation rate. These amounts exclude variable pass-through costs such as fuel and landing fees, among others. Based on these assumptions as of December 31, 2020, our future payments through the end of the terms of our CPAs are presented in the table below (in billions): 2021 $ 1.8 2022 1.8 2023 1.7 2024 1.5 2025 1.2 After 2025 3.1 $ 11.1 The actual amounts we pay to our regional operators under CPAs could differ materially from these estimates. For example, a 10% increase or decrease in scheduled block hours for all of United's regional operators (whether as a result of changes in average daily utilization or otherwise) in 2021 would result in a corresponding change in annual cash obligations under the CPAs of approximately $85 million.
Leases and Capacity Purchase Agreements	LEASES AND CAPACITY PURCHASE AGREEMENTSUnited leases aircraft, airport passenger terminal space, aircraft hangars and related maintenance facilities, cargo terminals, other airport facilities, other commercial real estate, office and computer equipment and vehicles, among other items. Certain of these leases include provisions for variable lease payments which are based on several factors, including, but not limited to, relative leased square footage, available seat miles, enplaned passengers, passenger facility charges, terminal equipment usage fees, departures, and airports' annual operating budgets. Due to the variable nature of the rates, these leases are not recorded on our balance sheet as a right-of-use asset and lease liability. For leases with terms greater than 12 months, we record the related right-of-use asset and lease liability at the present value of fixed lease payments over the lease term. To the extent a lease agreement includes an extension option that is reasonably certain to be exercised, we have recognized those amounts as part of our right-of-use assets and lease liabilities. Leases with an initial term of 12 months or less with purchase options or extension options that are not reasonably certain to be exercised are not recorded on the balance sheet; we recognize lease expense for these leases on a straight-line basis over the term of the lease. We combine lease and non-lease components, such as common area maintenance costs, in calculating the right-of-use assets and lease liabilities for all asset groups except for our CPAs, which contain embedded leases for regional aircraft. In addition to the lease component cost for regional aircraft, our CPAs also include non-lease components primarily related to the regional carriers' operating costs incurred in providing regional aircraft services. We allocate consideration for the lease components and non-lease components of each CPA based on their relative standalone values. Lease Cost . The Company's lease cost for the years ended December 31 included the following components (in millions): 2020 2019 2018 Operating lease cost $ 933 $ 1,038 $ 1,213 Variable and short-term lease cost 1,968 2,548 2,569 Amortization of finance lease assets 88 68 75 Interest on finance lease liabilities 16 85 44 Sublease income (23) (32) (38) Total lease cost $ 2,982 $ 3,707 $ 3,863 Lease terms and commitments . United's leases include aircraft leases for aircraft that are directly leased by United and aircraft that are operated by regional carriers on United's behalf under CPAs (but excluding aircraft owned by United) and non-aircraft leases. Aircraft operating leases relate to leases of 104 mainline and 290 regional aircraft while finance leases relate to leases of 37 mainline and 45 regional aircraft. United's aircraft leases have remaining lease terms of 1 month to 12 years with expiration dates ranging from 2021 through 2032. Under the terms of most aircraft leases, United has the right to purchase the aircraft at the end of the lease term, in some cases at fair market value, and in others, at a percentage of cost. Non-aircraft leases have remaining lease terms of 1 month to 32 years, with expiration dates ranging from 2021 through 2053. The table below summarizes the Company's scheduled future minimum lease payments under operating and finance leases, recorded on the balance sheet, as of December 31, 2020 (in millions): Operating Leases Finance Leases 2021 $ 847 $ 198 2022 693 59 2023 723 51 2024 704 47 2025 585 35 After 2025 3,979 64 Minimum lease payments 7,531 454 Imputed interest (1,933) (48) Present value of minimum lease payments 5,598 406 Less: current maturities of lease obligations (612) (182) Long-term lease obligations $ 4,986 $ 224 As of December 31, 2020, we have additional leases of approximately $740 million for several mainline aircraft, regional jets under a CPA and airport facilities and office space leases that have not yet commenced. These leases will commence in 2021 with lease terms of up to 12 years. In 2020, United entered into agreements with third parties to finance through sale and leaseback transactions new Boeing model 787-9 aircraft and Boeing model 737 MAX aircraft subject to purchase agreements between United and Boeing. In connection with the delivery of each aircraft from Boeing, United assigned its right to purchase such aircraft to the buyer, and simultaneous with the buyer's purchase from Boeing, United entered into a long-term lease for such aircraft with the buyer as lessor. Fifteen Boeing model aircraft were delivered in 2020 under these transactions (and each is presently subject to a long-term lease to United). Remaining aircraft in the agreements are scheduled to be delivered in 2021. Upon delivery of aircraft in these sale and leaseback transactions in 2020, the Company accounted for 11 of these aircraft, which have a repurchase option at a price other than fair value, as part of Flight equipment on the Company's balance sheet and the related obligation recorded in Other current liabilities and Other financial liabilities from sale-leasebacks (noncurrent) since they do not qualify for sale recognition. The remaining four aircraft that qualified for sale recognition were recorded as Operating lease right-of-use assets and Current/Long-term obligations under operating leases on the Company's balance sheet after recognition of related gains on such sale. See Note 14 of this report for additional information. Our lease agreements do not provide a readily determinable implicit rate nor is it available to us from our lessors. Instead, we estimate United's incremental borrowing rate based on information available at lease commencement in order to discount lease payments to present value. The table below presents additional information related to our leases as of December 31: 2020 2019 Weighted-average remaining lease term - operating leases 11 years 11 years Weighted-average remaining lease term - finance leases 4 years 6 years Weighted-average discount rate - operating leases 5.1 % 5.2 % Weighted-average discount rate - finance leases 4.4 % 5.7 % The table below presents supplemental cash flow information related to leases during the year ended December 31 (in millions): 2020 2019 2018 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows for operating leases $ 788 $ 902 $ 1,078 Operating cash flows for finance leases 20 70 53 Financing cash flows for finance leases 66 151 79 Regional CPAs. United has contractual relationships with various regional carriers to provide regional aircraft service branded as United Express. Under these CPAs, the Company pays the regional carriers contractually agreed fees (carrier costs) for operating these flights plus a variable rate adjustment based on agreed performance metrics, subject to annual adjustments. The fees are based on specific rates multiplied by specific operating statistics (e.g., block hours, departures), as well as fixed monthly amounts. Under these CPAs, the Company is also responsible for all fuel costs incurred, as well as landing fees and other costs, which are either passed through by the regional carrier to the Company without any markup or directly incurred by the Company. In some cases, the Company owns some or all of the aircraft subject to the CPA and leases such aircraft to the regional carrier. United's CPAs are for 475 regional aircraft as of December 31, 2020, and the CPAs have terms expiring through 2033. Aircraft operated under CPAs include aircraft leased directly from the regional carriers and those owned by United and operated by the regional carriers. See Part I, Item 2. Properties, of this report for additional information. In July 2020, the Company announced its plans to consolidate its Embraer ERJ 145 ("ERJ 145") operations into a single regional partner. As a result, the Company terminated its CPA with ExpressJet. ExpressJet flew its last commercial flight, on behalf of United, on September 30, 2020. Additionally, United transferred all of its ERJ 145 operations over to CommutAir as United's sole regional partner of this aircraft type. United recorded approximately $0.6 billion, $1.0 billion and $1.0 billion in expenses related to its CPAs with its regional carriers in which United is a minority shareholder, for the years ended December 31, 2020, 2019 and 2018, respectively. There were approximately $68 million and $69 million in accounts payable due to these companies as of December 31, 2020 and December 31, 2019, respectively. There were no material accounts receivables due from these companies as of December 31, 2020 and December 31, 2019. The CPAs with these related parties were executed in the ordinary course of business. Our future commitments under our CPAs are dependent on numerous variables, and are, therefore, difficult to predict. The most important of these variables is the number of scheduled block hours. Although we are not required to purchase a minimum number of block hours under certain of our CPAs, we have set forth below estimates of our future payments under the CPAs based on our assumptions. United's estimates of its future payments under all of the CPAs do not include the portion of the underlying obligation for any aircraft leased to a regional carrier or deemed to be leased from other regional carriers and facility rent that are disclosed as part of operating leases above. For purposes of calculating these estimates, we have assumed (1) the number of block hours flown is based on our anticipated level of flight activity or at any contractual minimum utilization levels if applicable, whichever is higher, (2) that we will reduce the fleet as rapidly as contractually allowed under each CPA, (3) that aircraft utilization, stage length and load factors will remain constant, (4) that each carrier's operational performance will remain at recent historic levels and (5) an annual projected inflation rate. These amounts exclude variable pass-through costs such as fuel and landing fees, among others. Based on these assumptions as of December 31, 2020, our future payments through the end of the terms of our CPAs are presented in the table below (in billions): 2021 $ 1.8 2022 1.8 2023 1.7 2024 1.5 2025 1.2 After 2025 3.1 $ 11.1 The actual amounts we pay to our regional operators under CPAs could differ materially from these estimates. For example, a 10% increase or decrease in scheduled block hours for all of United's regional operators (whether as a result of changes in average daily utilization or otherwise) in 2021 would result in a corresponding change in annual cash obligations under the CPAs of approximately $85 million.

Variable Interest Entities ("VI

Variable Interest Entities ("VIE")	12 Months Ended
	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Variable Interest Entities (VIE)	VARIABLE INTEREST ENTITIES ("VIE") Variable interests are contractual, ownership or other monetary interests in an entity that change with fluctuations in the fair value of the entity's net assets exclusive of variable interests. A VIE can arise from items such as lease agreements, loan arrangements, guarantees or service contracts. An entity is a VIE if (a) the entity lacks sufficient equity or (b) the entity's equity holders lack power or the obligation and right as equity holders to absorb the entity's expected losses or to receive its expected residual returns. If an entity is determined to be a VIE, the entity must be consolidated by the primary beneficiary. The primary beneficiary is the holder of the variable interests that has the power to direct the activities of a VIE that (i) most significantly impact the VIE's economic performance and (ii) has the obligation to absorb losses of or the right to receive benefits from the VIE that could potentially be significant to the VIE. Therefore, the Company must identify which activities most significantly impact the VIE's economic performance and determine whether it, or another party, has the power to direct those activities. Airport Leases . United is the lessee of real property under long-term operating leases at a number of airports where we are also the guarantor of approximately $1.9 billion of tax-exempt special facilities revenue bonds and interest thereon as of December 31, 2020. These leases are typically with municipalities or other governmental entities, which are excluded from the consolidation requirements concerning a VIE. To the extent United's leases and related guarantees are with a separate legal entity other than a governmental entity, United is not the primary beneficiary because the lease terms are consistent with market terms at the inception of the lease and the lease does not include a residual value guarantee, fixed-price purchase option, or similar feature. See Note 13 of this report for more information regarding United's guarantee of the tax-exempt special facilities revenue bonds. EETCs. United evaluated whether the pass-through trusts formed for its EETC financings, treated as either debt or aircraft operating leases, are VIEs required to be consolidated by United under applicable accounting guidance, and determined that the pass-through trusts are VIEs. Based on United's analysis as described below, United determined that it does not have a variable interest in the pass-through trusts. The primary risk of the pass-through trusts is credit risk (i.e. the risk that United, the issuer of the equipment notes, may be unable to make its principal and interest payments). The primary purpose of the pass-through trust structure is to enhance the credit worthiness of United's debt obligation through certain bankruptcy protection provisions, a liquidity facility (in certain of the EETC structures) and improved loan-to-value ratios for more senior debt classes. These credit enhancements lower United's total borrowing cost. Pass-through trusts are established to receive principal and interest payments on the equipment notes purchased by the pass-through trusts from United and remit these proceeds to the pass-through trusts' certificate holders. United does not invest in or obtain a financial interest in the pass-through trusts. Rather, United has an obligation to make interest and principal payments on its equipment notes held by the pass-through trusts. United does not intend to have any voting or non-voting equity interest in the pass-through trusts or to absorb variability from the pass-through trusts. Based on this analysis, the Company determined that it is not required to consolidate the pass-through trusts. BRW. Synergy's wholly-owned affiliate, BRW, is a special purpose entity created to be the borrower of the BRW Term Loan. BRW is also the owner of the collateral that secures the BRW Term Loan. BRW is a VIE and United holds variable interests in BRW including the BRW Term Loan. However, United is not the primary beneficiary of BRW because it does not hold BRW equity and does not have management rights at BRW and therefore does not have the power to direct the activities that most significantly impact BRW's economic performance. In connection with the delivery by United of a notice of default to BRW, Kingsland was granted, in accordance with the agreements related to the BRW Term Loan Agreement, authority to manage BRW. AVH. United concluded that AVH is a VIE and that United holds a variable interest through the AVH DIP Loan and a call option on BRW's AVH shares. However, United is not the primary beneficiary because it does not hold a material number of shares of AVH and does not have the power through the AVH DIP Loan Agreement or any other agreement to direct the activities that most significantly impact AVH's economic performance. Further, AVH is currently in Chapter 11 bankruptcy and as such the bankruptcy court is viewed as having power to direct the activities that most significantly impact AVH's economic performance. See Note 9 of this report for more information about the AVH call options. ManaAir . United concluded that ManaAir is a VIE as of December 31, 2020. United holds a variable interest in ManaAir in the form of equity interest, but United is not the primary beneficiary because it does not have power to direct the activities that most significantly impact ManaAir's economic performance. Champlain . United concluded that Champlain is a VIE as of December 31, 2020. United holds variable interests in Champlain in the form of equity interest and a loan to Champlain, but United is not the primary beneficiary because it does not have power to direct the activities that most significantly impact Champlain's economic performance.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Commitments. As of December 31, 2020 (adjusted to include the effects of the February 26, 2021 agreement with The Boeing Company ("Boeing") discussed below), United had firm commitments and options to purchase aircraft from Boeing, Airbus S.A.S. ("Airbus") and Embraer S.A. ("Embraer") presented in the table below: Scheduled Aircraft Deliveries Aircraft Type Number of Firm 2021 2022 After 2022 Airbus A321XLR 50 — — 50 Airbus A350 45 — — 45 Boeing 737 MAX 188 21 40 127 Boeing 787 11 11 — — Embraer E175 4 4 — — (a) United also has options and purchase rights for additional aircraft. On February 26, 2021, the Company entered into an agreement with The Boeing Company ("Boeing") for a firm order of 25 Boeing 737 MAX aircraft for delivery in 2023, and to reschedule the delivery of 40 previously ordered Boeing 737 MAX aircraft to 2022 and 5 Boeing 737 MAX aircraft into 2023. The aircraft listed in the table above are scheduled for delivery through 2030. To the extent the Company and the aircraft manufacturers with which the Company has existing orders for new aircraft agree to modify the contracts governing those orders, the amount and timing of the Company's future capital commitments could change. In March 2020, the Company entered into a confidential settlement with Boeing with respect to compensation for financial damages incurred in 2019 due to the grounding of the Boeing 737 MAX aircraft. In June 2020, the Company entered into an amended and restated confidential agreement with Boeing which provides for the settlement of additional items related to aircraft delivery and updates the scheduled delivery for substantially all undelivered Boeing 737 MAX aircraft. The compensation to the Company under the amended and restated settlement agreement is in the form of credit memos to be issued upon the satisfaction of certain conditions related to aircraft deliveries. The Company is accounting for this settlement as a reduction to the cost basis of future firm order Boeing 737 MAX aircraft deliveries and previously-delivered Boeing 737 MAX aircraft, which will reduce future depreciation expense associated with these aircraft. United also has an agreement to purchase 11 used Boeing 737-700 aircraft with expected delivery dates in 2021. In addition, United has an agreement to purchase 17 used Airbus A319 aircraft, which it intends to sell, with expected delivery dates in 2021 and 2022. The table below summarizes United's commitments as of December 31, 2020 (adjusted to include the effects of the February 26, 2021 agreement with Boeing), which include aircraft and related spare engines, aircraft improvements and all non-aircraft capital commitments (in billions): 2021 $ 4.9 2022 2.9 2023 2.8 2024 1.6 2025 2.0 After 2025 10.1 $ 24.3 Legal and Environmental. The Company has certain contingencies resulting from litigation and claims incident to the ordinary course of business. As of December 31, 2020, management believes, after considering a number of factors, including (but not limited to) the information currently available, the views of legal counsel, the nature of contingencies to which the Company is subject and prior experience, that the ultimate disposition of the litigation and claims will not materially affect the Company's consolidated financial position or results of operations. The Company records liabilities for legal and environmental claims when a loss is probable and reasonably estimable. These amounts are recorded based on the Company's assessments of the likelihood of their eventual disposition. Guarantees and Indemnifications. In the normal course of business, the Company enters into numerous real estate leasing and aircraft financing arrangements that have various guarantees included in the contracts. These guarantees are primarily in the form of indemnities under which the Company typically indemnifies the lessors and any tax/financing parties against liabilities that arise out of or relate to the use, operation or maintenance of the leased premises or financed aircraft. Currently, the Company believes that any future payments required under these guarantees or indemnities would be immaterial, as most liabilities and related indemnities are covered by insurance (subject to deductibles). Additionally, certain real estate leases include indemnities for any environmental liability that may arise out of or relate to the use of the leased premises. As of December 31, 2020, United is the guarantor of approximately $1.9 billion in aggregate principal amount of tax-exempt special facilities revenue bonds and interest thereon. These bonds, issued by various airport municipalities, are payable solely from rentals paid under long-term agreements with the respective governing bodies. The leasing arrangements associated with these obligations are accounted for as operating leases recognized on the Company's balance sheet with the associated expense recorded on a straight-line basis over the expected lease term. The obligations associated with these tax-exempt special facilities revenue bonds are included in our lease commitments disclosed in Note 11 of this report. All of these bonds are due between 2023 and 2038. In connection with funding the BRW Term Loan Agreement, the Company entered into an agreement with Kingsland, pursuant to which, in return for Kingsland's pledge of its 144.8 million common shares of AVH (which are eligible to be converted into the same number of preferred shares, which may be deposited with the depositary for AVH's ADRs, the class of AVH securities that trades on the NYSE, in exchange for 18.1 million ADRs) and its consent to BRW's pledge of its AVH common shares to United under the BRW Term Loan Agreement and related agreements, United (1) granted to Kingsland the right to put its AVH common shares to United at market price on the fifth anniversary of the BRW Term Loan Agreement or upon certain sales of AVH common shares owned by BRW, including upon a foreclosure of United's security interest or any completed liquidation or dissolution of AVH, and (2) guaranteed BRW's obligation to pay Kingsland the difference (which amount, if paid by United, any such sale, as applicable, is less than $12 per ADR on the NYSE, for an aggregate maximum possible combined put payment and guarantee amount on the fifth anniversary of $217 million. Due to AVH's financial uncertainty due to its high level of leverage and the fact that the airline had ceased operations due to the COVID-19 pandemic, the Company recorded the full amount under this guarantee as a liability. In November 2020, the Company posted $217 million as cash collateral for a standby letter of credit in favor of Citibank, N.A. that serves as security for a loan from Citibank to Kingsland. Any drawings under the letter of credit would offset the Company's maximum possible put and guarantee payment to Kingsland by an equal amount. The posting of this collateral, and any potential credit against the Company's put and guarantee payment, are entirely related to the original transactions entered in 2018 and do not represent any new or incremental investment. As of December 31, 2020, United is the guarantor of $119 million of aircraft mortgage debt issued by one of United's regional carriers. The aircraft mortgage debt is subject to similar increased cost provisions as described below for the Company's debt, and the Company would potentially be responsible for those costs under the guarantees. As of December 31, 2020, United had $380 million of surety bonds securing various insurance related obligations with expiration dates through 2024. Increased Cost Provisions. In United's financing transactions that include loans in which United is the borrower, United typically agrees to reimburse lenders for any reduced returns with respect to the loans due to any change in capital requirements and, in the case of loans with respect to which the interest rate is based on LIBOR, for certain other increased costs that the lenders incur in carrying these loans as a result of any change in law, subject, in most cases, to obligations of the lenders to take certain limited steps to mitigate the requirement for, or the amount of, such increased costs. At December 31, 2020, the Company had $9.8 billion of floating rate debt with remaining terms of up to 12 years that are subject to these increased cost provisions. In several financing transactions involving loans or leases from non-U.S. entities, with remaining terms of up to 12 years and an aggregate balance of $8.3 billion, the Company bears the risk of any change in tax laws that would subject loan or lease payments thereunder to non-U.S. entities to withholding taxes, subject to customary exclusions. Fuel Consortia. United participates in numerous fuel consortia with other air carriers at major airports to reduce the costs of fuel distribution and storage. Interline agreements govern the rights and responsibilities of the consortia members and provide for the allocation of the overall costs to operate the consortia based on usage. The consortia (and in limited cases, the participating carriers) have entered into long-term agreements to lease certain airport fuel storage and distribution facilities that are typically financed through tax-exempt bonds, either special facilities lease revenue bonds or general airport revenue bonds, issued by various local municipalities. In general, each consortium lease agreement requires the consortium to make lease payments in amounts sufficient to pay the maturing principal and interest payments on the bonds. As of December 31, 2020, approximately $2.3 billion principal amount of such bonds were secured by significant fuel facility leases in which United participates, as to which United and each of the signatory airlines has provided indirect guarantees of the debt. As of December 31, 2020, the Company's contingent exposure was approximately $293 million principal amount of such bonds based on its recent consortia participation. The Company's contingent exposure could increase if the participation of other air carriers decreases. The guarantees will expire when the tax-exempt bonds are paid in full, which ranges from 2022 to 2051. The Company did not record a liability at the time these indirect guarantees were made. Regional Capacity Purchase. As of December 31, 2020, United had 303 call options to purchase regional jet aircraft being operated by certain of its regional carriers with contract dates extending until 2029. These call options are exercisable upon wrongful termination or breach of contract, among other conditions. Credit Card Processing Agreements. The Company has agreements with financial institutions that process customer credit card transactions for the sale of air travel and other services. Under certain of the Company's credit card processing agreements, the financial institutions in certain circumstances have the right to require that the Company maintain a reserve equal to a portion of advance ticket sales that has been processed by that financial institution, but for which the Company has not yet provided the air transportation. Such financial institutions may require additional cash or other collateral reserves to be established or additional withholding of payments related to receivables collected if the Company does not maintain certain minimum levels of unrestricted cash, cash equivalents and short-term investments (collectively, "Unrestricted Liquidity"). The Company's current level of Unrestricted Liquidity is substantially in excess of these minimum levels. Labor Negotiations. As of December 31, 2020, United, including its subsidiaries, had approximately 74,400 employees. Approximately 84% of United's employees were represented by various U.S. labor organizations. On February 1, 2019, the collective bargaining agreement with the Air Line Pilots Association ("ALPA"), the labor union representing United's pilots, became amendable. The Company and ALPA are in negotiations for an amended agreement. On September 28, 2020, United's pilots approved an agreement to avoid furloughs, at least until June 2021. The agreement offered, among other things, an early separation option for certain eligible pilots. The Company and UNITE HERE, the labor union representing United's Catering Operations employees, started negotiations for a first collective bargaining agreement in March 2019. In December 2020, the Company reviewed the provision of the collective bargaining agreement with the International Brotherhood of Teamsters ("IBT") for alignment with contract terms with other airlines' workgroups. This review provided a base pay rate increase for employees covered under this agreement.

Special Charges and Unrealized

Special Charges and Unrealized (Gains) Losses on Investments	12 Months Ended
	Dec. 31, 2020
Restructuring and Related Activities [Abstract]
SPECIAL CHARGES AND UNREALIZED (GAINS) LOSSES ON INVESTMENTS	SPECIAL CHARGES AND UNREALIZED (GAINS) LOSSES ON INVESTMENTS Special charges and unrealized gains and losses on investments in the statements of consolidated operations consisted of the following for the years ended December 31 (in millions): Operating: 2020 2019 2018 CARES Act grant $ (3,536) $ — $ — Severance and benefit costs 575 16 41 Impairment of assets 318 171 377 Termination of an engine maintenance service agreement — — 64 (Gains) losses on sale of assets and other special charges 27 59 5 Total operating special charges (credit) (2,616) 246 487 Nonoperating credit loss on BRW Term Loan and related guarantee 697 — — Nonoperating special termination benefits and settlement losses 687 — — Nonoperating unrealized (gains) losses on investments 194 (153) 5 Total nonoperating special charges and unrealized (gains) losses on investments 1,578 (153) 5 Total operating and nonoperating special charges (credit) and unrealized (gains) losses on investments (1,038) 93 492 Income tax expense (benefit), net of valuation allowance 404 (21) (110) Income tax adjustments (Note 6) — — (5) Total operating and nonoperating special charges (credit) and unrealized (gains) losses on investments, net of income taxes $ (634) $ 72 $ 377 2020 CARES Act grant. During 2020, the Company received approximately $5.1 billion in funding pursuant to the Payroll Support Program under the CARES Act, which consisted of a $3.6 billion grant and a $1.5 billion unsecured loan. The Company recorded $66 million for warrants issued to Treasury, within stockholders' equity, as an offset to the grant income. For 2020, we recognized the $3.5 billion grant as a credit to Special charges (credit). Severance and benefit costs . In July 2020, the Company started the involuntary furlough process by issuing WARN Act notices to approximately 36,000 of its employees. Since then, the Company worked to reduce the total number of furloughs to approximately 13,000 employees by working closely with its union partners, introducing new voluntary options selected by approximately 9,000 employees and proposing creative solutions that would save jobs. This workforce reduction is part of the Company's strategic realignment of its business and new organizational structure as a result of the impacts of the COVID-19 pandemic on the Company's operations and cost structure. The Company recorded $575 million during 2020 related to the workforce reduction, employee severance, pay continuance from voluntary retirements, and benefits-related costs (and additional costs associated with special termination benefits and settlement losses discussed below under "Nonoperating special termination benefits and settlement losses"). See also Note 7 of this report for further information. Impairment of assets . United assesses its goodwill and intangible assets for potential impairment on an annual basis as of October 1, and on an interim basis if there are indicators that an impairment of goodwill or the intangible assets may have occurred. For goodwill and certain of its intangible assets, including the Company's China routes, London-Heathrow slots, alliances and the United trade name and logo, the Company performed a quantitative assessment which involved determining the fair value of the asset and comparing that amount to the asset's carrying value and, in the case of goodwill, comparing the Company's fair value to its carrying value. For all other intangible assets, the Company performed a qualitative assessment of whether it was more likely than not that an impairment had occurred. To determine fair value, the Company used discounted cash flow methods appropriate for each asset. Key inputs into the models included forecasted capacity, revenues, fuel costs, other operating costs and an overall discount rate. The assumptions used for future projections include that demand will likely remain suppressed through 2021. These assumptions are inherently uncertain as they relate to future events and circumstances. The Company performed intangible asset impairment reviews throughout the year. In light of the ongoing impact of the COVID-19 pandemic on both the U.S. and global economies, the significant, sustained impact on the demand for travel and government policies that restrict air travel, the exact timing of the recovery from the COVID-19 pandemic, and the speed at which such recovery could occur, continues to remain uncertain and could result in additional impairment charges in the future. We expect to continue to modify our cost management structure and capacity as the timing of demand recovery becomes more certain. As a result of the impairment assessments, the Company recorded impairment charges of $130 million during 2020 for its China routes which was primarily caused by the COVID-19 pandemic, the Company's subsequent suspension of flights to China and a further delay in the expected return of full capacity to the China markets. The Company's China routes are subject to China slot usage rules and U.S. Department of Transportation frequency use requirements. For the summer and winter 2020 seasons, both governments issued relief from these rules. The Company, therefore, has been able to reduce its mainland China service without violating the governments' rules. The Company is advocating for a continuation of this relief through the summer 2021 season. United assesses its long-lived assets whenever there are indicators that an impairment of the assets may have occurred. During 2020, in response to decreased demand caused by the COVID-19 pandemic, the Company temporarily grounded certain of its mainline fleet, some of which continue to be temporarily grounded. United performed forecasted cash flow analyses and determined that the carrying value of the tested fleets is recoverable from future cash flows expected to be generated by those fleets. To determine whether impairments exist for active and temporarily parked mainline aircraft, we group assets at the fleet-type level. In the fourth quarter of 2020, the Company permanently grounded 11 of its Boeing 757-200 aircraft. The Company's decision was influenced by the FAA's rescission of the order that grounded the Boeing 737MAX aircraft in March of 2019. As a result of the cash flow analysis for the 11 permanently-grounded aircraft, we recorded $94 million of impairments related to those aircraft and the related engines and spare parts. During 2020, the Company recorded an impairment of $38 million of the right-of-use asset associated with the embedded aircraft lease in one of our CPAs. We measure cash flows at the contract level with our CPA partners. This impairment was primarily due to the impact to cash flows from the pandemic and the relatively short remaining term under the CPA. During 2020, the Company also recorded $56 million of impairments related to various cancelled facility, aircraft induction and information technology capital projects. The decisions driving these impairments were the result of the COVID-19 pandemic's impact on our operations. To the extent we make future decisions to permanently ground any of our fleet, or our estimates of future cash flows generated by our fleet change, we may be required to record impairment charges in future periods. The aircraft and intangible asset impairments described above required Level 3 fair value inputs including the maintenance condition of the aircraft (for impaired aircraft) and future assumptions about profit margin and our weighted average cost of capital (for the China route intangible). Nonoperating special termination benefits and settlement losses. During 2020, the Company recorded $687 million of settlement losses related to the Company's primary defined benefit pension plan covering certain U.S. non-pilot employees, and special termination benefits offered, under furlough and voluntary separation programs. See Note 7 of this report for additional information. Nonoperating unrealized gains (losses) on investments, net. During 2020, the Company recorded losses of $170 million primarily for changes in the fair value of its investment in Azul. Also during 2020, the Company recorded losses of $24 million for the decrease in fair value of the AVH Derivative Assets. Nonoperating credit loss on BRW Term Loan and related guarantee. During 2020, the Company recorded a $697 million expected credit loss allowance for the BRW Term Loan and related guarantee. AVH is currently in bankruptcy. See Notes 8 and 13 of this report for additional information. 2019 During 2019, the Company recorded a special non-cash impairment charge of $90 million associated with its Hong Kong routes. The Company determined the fair value of the Hong Kong routes using a variation of the income approach known as the excess earnings method, which discounts an asset's projected future net cash flows to determine the current fair value. During 2019, the Company recorded a $43 million impairment primarily for surplus Boeing 767 aircraft engines removed from operations, an $18 million charge primarily for the write-off of unexercised aircraft purchase options, and $20 million in other aircraft impairments. During 2019, the Company recorded $14 million of management severance and $2 million of severance and benefit costs related to a voluntary early-out program for its technicians and related employees represented by the IBT. In the first quarter of 2017, approximately 1,000 technicians and related employees elected to voluntarily separate from the Company and received a severance payment, with a maximum value of $100,000 per participant, based on years of service, with retirement dates through early 2019. During 2019, the Company recorded charges of $25 million related to contract terminations, $18 million for the settlement of certain legal matters, $14 million for costs related to the transition of fleet types within a regional carrier contract and $2 million of other charges. During 2019, the Company recorded gains of $140 million for the change in market value of certain of its equity investments, primarily Azul, and $13 million for the change in fair value of the AVH Derivative Assets. 2018 During 2018, the Company recorded a special non-cash impairment charge of $206 million associated with its Hong Kong routes as a result of its annual intangible assets impairment review. The Company determined the fair value of the Hong Kong routes using a variation of the income approach as described above for the 2019 Hong Kong impairment. In May 2018, the Brazil–United States open skies agreement was ratified, which provides air carriers with unrestricted access between the United States and Brazil. The Company determined that the approval of the open skies agreement impaired the entire value of its Brazil route authorities because the agreement removes all limitations or reciprocity requirements for flights between the United States and Brazil. Accordingly, the Company recorded a $105 million special charge to write off the entire value of the intangible asset associated with its Brazil routes. Also during 2018, the Company recorded $66 million of fair value adjustments related to aircraft purchased off lease, write-offs of unexercised aircraft purchase options and other impairments related to certain fleet types and international slots no longer in use. During 2018, the Company recorded $22 million of severance and benefit costs related to the voluntary early-out program for its technicians and related employees represented by the IBT as described above. Also during 2018, the Company recorded other management severance of $19 million. During 2018, the Company recorded a one-time termination charge of $64 million related to one of its engine maintenance service agreements. During 2018, the Company recorded gains of $28 million for the change in market value of certain of its equity investments, primarily Azul. Also, the Company recorded losses of $33 million for the change in fair value of the AVH Derivative Assets.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) Quarter Ended (In millions, except per share amounts) March 31 June 30 September 30 December 31 2020 Operating revenue $ 7,979 $ 1,475 $ 2,489 $ 3,412 Loss from operations (972) (1,637) (1,615) (2,135) Net loss (1,704) (1,627) (1,841) (1,897) Basic and diluted loss per share (6.86) (5.79) (6.33) (6.39) 2019 Operating revenue $ 9,589 $ 11,402 $ 11,380 $ 10,888 Income from operations 495 1,472 1,473 861 Net income 292 1,052 1,024 641 Basic earnings per share 1.09 4.03 4.01 2.54 Diluted earnings per share 1.09 4.02 3.99 2.53 UAL's quarterly financial data is subject to seasonal fluctuations and historically its second and third quarter financial results, which reflect higher travel demand, are better than its first and fourth quarter financial results. UAL's quarterly results were impacted by the following significant items (in millions): Quarter Ended March 31 June 30 September 30 December 31 2020 CARES Act grant $ — $ (1,589) $ (1,494) $ (453) Impairment of assets 50 80 51 137 Severance and benefit costs — 63 350 162 (Gains) losses on sale of assets and other special charges 13 (3) 12 5 Total operating special charges (credit) 63 (1,449) (1,081) (149) Nonoperating special termination benefits and settlement losses — 231 415 41 Nonoperating unrealized (gains) losses on investments 319 (9) (15) (101) Nonoperating credit loss on BRW Term Loan and related guarantee 697 — — — Total nonoperating special charges and unrealized (gains) losses on investments 1,016 222 400 (60) Total operating and nonoperating special charges (credit) and unrealized (gains) losses on investments 1,079 (1,227) (681) (209) Income tax expense (benefit), net of valuation allowance (14) 241 148 29 Total operating and nonoperating special charges (credit) and unrealized (gains) losses on investments, net of income taxes $ 1,065 $ (986) $ (533) $ (180) 2019 Impairment of assets $ 8 $ 61 $ — $ 102 Severance and benefit costs 6 6 2 2 (Gains) losses on sale of assets and other special charges 4 4 25 26 Total operating special charges 18 71 27 130 Nonoperating unrealized (gains) losses on investments (17) (34) (21) (81) Total special charges and unrealized (gains) losses on investments 1 37 6 49 Income tax benefit related to special charges and unrealized (gains) losses on investments — (8) (2) (11) Total special charges and unrealized (gains) losses on investments, net of income tax $ 1 $ 29 $ 4 $ 38 See Note 14 of this report for additional information related to these items.

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2020
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule II - Valuation and Qualifying Accounts	Schedule II Valuation and Qualifying Accounts For the Years Ended December 31, 2020, 2019 and 2018 (In millions) Description Balance at Additions Deductions Other Balance at Allowance for credit losses - receivables: 2020 $ 9 $ 70 $ 16 $ 15 $ 78 2019 8 17 16 — 9 2018 7 17 16 — 8 Obsolescence allowance—spare parts: 2020 $ 425 $ 88 $ 35 $ — $ 478 2019 412 76 63 — 425 2018 354 73 15 — 412 Allowance for credit losses - notes receivable: 2020 $ — $ 518 $ — $ 4 $ 522 Valuation allowance for deferred tax assets: 2020 $ 58 $ 197 $ 8 $ — $ 247 2019 59 — 1 — 58 2018 63 2 6 — 59

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates— The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America ("GAAP") requires management to make estimates and assumptions that affect the amounts reported in these financial statements and accompanying notes. Actual results could differ from those estimates.
Revenue Recognition	Revenue Recognitio n— The Company presents Passenger revenue, Cargo revenue and Other operating revenue on its income statement. Passenger revenue is recognized when transportation is provided and Cargo revenue is recognized when shipments arrive at their destination. Other operating revenue is recognized as the related performance obligations are satisfied. Passenger tickets and related ancillary services sold by the Company for flights are purchased primarily via credit card transactions, with payments collected by the Company in advance of the performance of related services. The Company initially records ticket sales in its Advance ticket sales liability, deferring revenue recognition until the travel occurs. For travel that has more than one flight segment, the Company deems each segment as a separate performance obligation and recognizes revenue for each segment as travel occurs. Tickets sold by other airlines where the Company provides the transportation are recognized as passenger revenue at the estimated value to be billed to the other airline when travel is provided. Differences between amounts billed and the actual amounts may be rejected and rebilled or written off if the amount recorded was different from the original estimate. When necessary, the Company records a reserve against its billings and payables with other airlines based on historical experience. The Company sells certain tickets with connecting flights with one or more segments operated by its other airline partners. For segments operated by its other airline partners, the Company has determined that it is acting as an agent on behalf of the other airlines as they are responsible for their portion of the contract (i.e. transportation of the passenger). The Company, as the agent, recognizes revenue within Other operating revenue at the time of the travel for the net amount representing commission to be retained by the Company for any segments flown by other airlines. Refundable tickets expire after one year from the date of issuance. Non-refundable tickets generally expire on the date of the intended travel, unless the date is extended by notification from the customer on or before the intended travel date. In April 2020, due to the COVID-19 pandemic, the Company extended the expiration dates on all passenger tickets issued between May 1, 2019 and March 31, 2020 to 24 months from the original issue date. On February 24, 2021, the Company extended the expiration dates for all tickets issued between May 1, 2019 and March 31, 2021 to March 31, 2022. Fees charged in association with changes or extensions to non-refundable tickets are considered part of the Company's passenger travel obligation. As such, those fees are deferred at the time of collection and recognized at the time the travel is provided. Effective August 30, 2020, the Company eliminated change fees on all standard Economy and Premium cabin tickets for travel within the 50 U.S. states, Washington, D.C., Puerto Rico and the U.S. Virgin Islands. Also, in December 2020, the Company eliminated change fees on flights from the U.S. to all international destinations and fees on Basic Economy and all other international travel tickets issued by March 31, 2021. United initially capitalizes the costs of selling airline travel tickets and then recognizes those costs as Distribution expense at the time of travel. Passenger ticket costs include credit card fees, travel agency and other commissions paid, as well as global distribution systems booking fees. Advance Ticket Sales. Advance ticket sales represent the Company's liability to provide air transportation in the future. All tickets sold at any given point of time have travel dates extending up to 12 months. The Company defers amounts related to future travel in its Advance ticket sales liability account. The Company's Advance ticket sales liability also includes credits issued to customers on electronic travel certificates ("ETCs") and future flight credits ("FFCs"), primarily for ticket cancellations, which can be applied towards a purchase of a new ticket. In April 2020, due to the COVID-19 pandemic, the Company extended the expiration dates of ETCs from 12 months from the date of issuance to 24 months from the date of issuance and extended the expiration of FFCs, for tickets issued between May 1, 2019 and March 31, 2020 to 24 months from the original issue date. On February 24, 2021, the Company extended the expiration dates for all tickets issued between May 1, 2019 and March 31, 2021 to March 31, 2022. As of December 31, 2020, the Company's Advance ticket sales liability included $3.1 billion related to these credits and approximately 74% of these credits have expiration dates extending beyond 12 months. The Company records breakage revenue on the travel date for its estimate of tickets that will expire unused. To determine breakage, the Company uses its historical experience with refundable and nonrefundable expired tickets and other facts, such as recent aging trends, program changes and modifications that could affect the ultimate expiration patterns of tickets. The Company continues to use its historical experience and most recent trends and program changes to estimate its breakage. The Company will update its breakage estimates as future information is received. Given the uncertainty of travel demand caused by COVID-19, a significant portion of the $3.1 billion related to the ETCs and FFCs may expire unused in future periods and get recognized as breakage. Also, the Company is unable to estimate the amount of the ETCs and FFCs that will be used within the next 12 months and has classified the entire amount of the Advanced ticket liability in current liabilities even though some of the ETCs and FFCs could be used after the next 12 months. In the years ended December 31, 2020, 2019 and 2018, the Company recognized approximately $3.0 billion, $3.4 billion and $3.1 billion, respectively, of passenger revenue for tickets that were included in Advance ticket sales at the beginning of those periods. Revenue by Geography. The Company further disaggregates revenue by geographic regions. Operating segments are defined as components of an enterprise with separate financial information, which are evaluated regularly by the chief operating decision maker and are used in resource allocation and performance assessments. The Company deploys its aircraft across its route network through a single route scheduling system to maximize its value. When making resource allocation decisions, the Company's chief operating decision maker evaluates flight profitability data, which considers aircraft type and route economics. The Company's chief operating decision maker makes resource allocation decisions to maximize the Company's consolidated financial results. Managing the Company as one segment allows management the opportunity to maximize the value of its route network. Ancillary Fees.
Ticket Taxes	Ticket Taxes— Certain governmental taxes are imposed on the Company's ticket sales through a fee included in ticket prices. The Company collects these fees and remits them to the appropriate government agency. These fees are recorded on a net basis and, as a result, are excluded from revenue. The CARES Act provided an excise tax holiday that suspended certain U.S. aviation excise taxes. The excise tax holiday began on March 28, 2020 and ended on December 31, 2020. During the excise tax holiday, no excise tax was imposed on amounts paid for the transportation of persons and property by air. At December 31, 2020, the Company had approximately $150 million of excise taxes refunded to customers that are to be reimbursed by the U.S. government in 2021.
Frequent Flyer Accounting	Frequent Flyer Accounting— United's MileagePlus loyalty program builds customer loyalty by offering awards, benefits and services to program participants. Members in this program earn miles for travel on United, United Express, Star Alliance members and certain other airlines that participate in the program. Members can also earn miles by purchasing goods and services from our network of non-airline partners. We have contracts to sell miles to these partners with the terms extending from one Miles Earned in Conjunction with Travel. When frequent flyers earn miles for flights, the Company recognizes a portion of the ticket sales as revenue when the travel occurs and defers a portion of the ticket sale representing the value of the related miles as a separate performance obligation. The Company determines the estimated selling price of travel and miles as if each element is sold on a separate basis. The total consideration from each ticket sale is then allocated to each of these elements, individually, on a pro-rata basis. At the time of travel, the Company records the portion allocated to the miles to Frequent flyer deferred revenue on the Company's consolidated balance sheet and subsequently recognizes it into revenue when miles are redeemed for air travel and non-air travel awards. Estimated Selling Price of Miles . The Company's estimated selling price of miles is based on an equivalent ticket value, which incorporates the expected redemption of miles, as the best estimate of selling price for these miles. The equivalent ticket value is based on the prior 12 months' weighted average equivalent ticket value of similar fares as those used to settle award redemptions while taking into consideration such factors as redemption pattern, cabin class, loyalty status and geographic region. The estimated selling price of miles is adjusted by breakage that considers a number of factors, including redemption patterns of various customer groups. Estimate of Miles Not Expected to be Redeemed ("Breakage") . The Company's breakage model is based on the assumption that the likelihood that an account will redeem its miles can be estimated based on a consideration of the account's historical behavior. The Company uses a logit regression model to estimate the probability that an account will redeem its current miles balance. The Company reviews its breakage estimates annually based upon the latest available information. The Company's estimate of the expected breakage of miles requires significant management judgment. Current and future changes to breakage assumptions, or to program rules and program redemption opportunities, may result in material changes to the deferred revenue balance as well as recognized revenues from the program. For the portion of the outstanding miles that we estimate will not be redeemed, we recognize the associated value proportionally as the remaining miles are redeemed. Co-Brand Agreement . During 2020, the Company entered into a Third Amended and Restated Co-Branded Card Marketing Services Agreement (as amended from time to time, the "Co-Brand Agreement") with its co-branded credit card partner JPMorgan Chase Bank, N.A. ("Chase"). The Co-Brand Agreement extended the term of the agreement into 2029 and modified certain other terms, resulting in a different allocation among the separately identifiable performance obligations. Chase awards miles to MileagePlus members based on their credit card activity. United identified the following significant separately identifiable performance obligations in the Co-Brand Agreement: • MileagePlus miles awarded – United has a performance obligation to provide MileagePlus cardholders with miles to be used for air travel and non-travel award redemptions. The Company records Passenger revenue related to the travel awards when the transportation is provided and records Other revenue related to the non-travel awards when the goods or services are delivered. The Company records the cost associated with non-travel awards in Other operating revenue, as an agent. • Marketing – United has a performance obligation to provide Chase access to United's customer list and the use of United's brand. Marketing revenue is recorded to Other operating revenue as miles are delivered to Chase. • Advertising – United has a performance obligation to provide advertising in support of the MileagePlus card in various customer contact points such as United's website, email promotions, direct mail campaigns, airport advertising and in-flight advertising. Advertising revenue is recorded to Other operating revenue as miles are delivered to Chase. • Other travel-related benefits – United's performance obligations are comprised of various items such as waived bag fees, seat upgrades and lounge passes. Lounge passes are recorded to Other operating revenue as customers use the lounge passes. Bag fees and seat upgrades are recorded to Passenger revenue at the time of the associated travel. We account for all the payments received (including monthly and one-time payments) under the Co-Brand Agreement by allocating them to the separately identifiable performance obligations. The fair value of the separately identifiable performance obligations is determined using management's estimated selling price of each component. The objective of using the estimated selling price based methodology is to determine the price at which we would transact a sale if the product or service were sold on a stand-alone basis. Accordingly, we determine our best estimate of selling price by considering multiple inputs and methods including, but not limited to, discounted cash flows, brand value, volume discounts, published selling prices, number of miles awarded and number of miles redeemed. The Company estimated the selling prices and volumes over the term of the Co-Brand Agreement in order to determine the allocation of proceeds to each of the components to be delivered. We also evaluate volumes on an annual basis, which may result in a change in the allocation of the estimated consideration from the Co-Brand Agreement on a prospective basis.
Cash and Cash Equivalents and Restricted Cash	Cash and Cash Equivalents and Restricted Cash— Highly liquid investments with a maturity of three months or less on their acquisition date are classified as cash and cash equivalents. Restricted cash-current— primarily includes $217 million cash collateral for a standby letter of credit associated with guarantees under the BRW Term Loan. See Note 8 of this report for additional information on the BRW Term Loan and Note 13 for additional information on the guarantee. The balance also includes amounts to be used for the payment of fees, principal and interest on the $6.8 billion of senior secured notes and a secured term loan facility (the "MileagePlus Financing") secured by substantially all of the assets of Mileage Plus Holdings, LLC ("MPH"), a direct wholly-owned subsidiary of United. Restricted cash-non-current— primarily includes collateral associated with the MileagePlus Financing, collateral for letters of credit and collateral associated with facility leases and other insurance-related obligations. Restricted cash is classified as short-term or long-term in the consolidated balance sheets based on the expected timing of return of the assets to the Company or payment to an outside party.
Investments	Investments— Debt investments are classified as available-for-sale and are stated at fair value. Realized gains and losses on sales of these investments are reflected in Miscellaneous, net in the consolidated statements of operations. Unrealized gains and losses on available-for-sale securities are reflected as a component of accumulated other comprehensive income (loss). Equity investments with readily determinable fair values are measured at fair value. Equity investments without readily determinable fair values are measured using the equity method, or measured at cost with adjustments for observable changes in price or impairments (referred to as the measurement alternative). Changes in fair value are recorded in Unrealized gains (losses) on investments, net in the consolidated statements of operations. See Note 9 of this report for additional information related to investments.
Accounts Receivable	Accounts Receivable—Accounts receivable primarily consist of amounts due from credit card companies, non-airline partners, and cargo customers. We provide an allowance for uncollectible accounts equal to the estimated losses expected to be incurred based on historical write-offs and other specific analyses.
Aircraft Fuel, Spare Parts and Supplies	Aircraft Fuel, Spare Parts and Supplies— The Company accounts for aircraft fuel, spare parts and supplies at average cost and provides an obsolescence allowance for aircraft spare parts with an assumed residual value of 10% of original cost.
Property and Equipment	Property and Equipment— The Company records additions to owned operating property and equipment at cost when acquired. Property under finance leases and the related obligation for future lease payments are recorded at an amount equal to the initial present value of those lease payments. Modifications that enhance the operating performance or extend the useful lives of airframes or engines are capitalized as property and equipment. We periodically receive credits in connection with the acquisition of aircraft and engines including those related to contractual damages related to delays in delivery. These credits are deferred until the aircraft and engines are delivered, and then applied as a reduction to the cost of the related equipment.
Long-Lived Asset Impairments	Long-Lived Asset Impairments— The Company evaluates the carrying value of long-lived assets subject to amortization whenever events or changes in circumstances indicate that an impairment may exist. For purposes of this testing, the Company has generally identified the aircraft fleet type as the lowest level of identifiable cash flows for its mainline fleet and the contract level for its regional fleet under capacity purchase agreements ("CPAs"). An impairment charge is recognized when the asset's carrying value exceeds its net undiscounted future cash flows. The amount of the charge is the difference between the asset's carrying value and fair market value.
Intangibles	Intangibles— The Company has finite-lived and indefinite-lived intangible assets, including goodwill. Finite-lived intangible assets are amortized over their estimated useful lives. Goodwill and indefinite-lived intangible assets are not amortized but are reviewed for impairment on an annual basis as of October 1, or more frequently if events or circumstances indicate that the asset may be impaired.
Labor Costs	Labor Costs— The Company records expenses associated with new or amendable labor agreements when the amounts are probable and estimable. These include costs associated with lump sum cash payments that would be made in conjunction with the ratification of labor agreements. To the extent these upfront costs are in lieu of future pay increases, they would be capitalized and amortized over the term of the labor agreements. If not, these amounts would be expensed.
Share-Based Compensation	Share-Based Compensation— The Company measures the cost of employee services received in exchange for an award of equity instruments based on the grant date fair value of the award. The resulting cost is recognized over the period during which an employee is required to provide service in exchange for the award, usually the vesting period. Obligations for cash-settled restricted stock units ("RSUs") are remeasured at fair value throughout the requisite service period at the close of the reporting period based upon UAL's stock price. In addition to the service requirement, certain RSUs have performance metrics that must be achieved prior to vesting. These awards are accrued based on the expected level of achievement at each reporting period. An adjustment is recorded each reporting period to adjust compensation expense based on the then current level of expected performance achievement for the performance-based awards. See Note 4 of this report for additional information on UAL's share-based compensation plans.
Maintenance and Repairs	Maintenance and Repairs— The cost of maintenance and repairs, including the cost of minor replacements, is charged to expense as incurred, except for costs incurred under our power-by-the-hour ("PBTH") engine maintenance agreements. PBTH contracts transfer certain risk to third-party service providers and fix the amount we pay per flight hour or per cycle to the service provider in exchange for maintenance and repairs under a predefined maintenance program. Under PBTH agreements, the Company recognizes expense at a level rate per engine hour, unless the level of service effort and the related payments during the period are substantially consistent, in which case the Company recognizes expense based on the amounts paid.
Advertising	Advertising—Advertising costs, which are included in Other operating expenses, are expensed as incurred.
Third-Party Business	Third-Party Business— The Company has third-party business revenue that includes catering, ground handling, maintenance services and frequent flyer award non-travel redemptions. Third-party business revenue is recorded in Other operating revenue. The Company also incurs third-party business expenses, such as maintenance, ground handling and catering services for third parties and non-travel mileage redemptions. The third-party business expenses are recorded in Other operating expenses, except for non-travel mileage redemption. Non-travel mileage redemption expenses are recorded to Other operating revenue.
Uncertain Income Tax Positions	Uncertain Income Tax Positions—The Company has recorded reserves for income taxes and associated interest that may become payable in future years. Although management believes that its positions taken on income tax matters are reasonable, the Company nevertheless established tax and interest reserves in recognition that various taxing authorities may challenge certain of the positions taken by the Company, potentially resulting in additional liabilities for taxes and interest. The Company's uncertain tax position reserves are reviewed periodically and are adjusted as events occur that affect its estimates, such as the availability of new information, the lapsing of applicable statutes of limitation, the conclusion of tax audits, the measurement of additional estimated liability, the identification of new tax matters, the release of administrative tax guidance affecting its estimates of tax liabilities, or the rendering of relevant court decisions. The Company records penalties and interest relating to uncertain tax positions as part of income tax expense in its consolidated statements of operations.
Recently Issued Accounting Standards	Recently Issued Accounting Standards— The Company adopted Accounting Standards Update No. 2016-13 Financial Instruments—Credit Losses ("ASU 2016-13") effective January 1, 2020. ASU 2016-13 replaces the incurred loss methodology with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to calculate credit loss estimates. For trade receivables, loans and held-to-maturity debt securities, entities are required to estimate lifetime expected credit losses. For available-for-sale debt securities, entities are required to recognize an allowance for credit losses rather than a reduction to the carrying value of the asset. The Company recorded a $17 million cumulative-effect adjustment, net of related income taxes, to its retained earnings balance on January 1, 2020 as a result of this adoption. See Notes 8, 13 and 14 of this report for additional disclosures about the impact of ASU 2016-13 on 2020 results.
Fair Value Information	Accounting standards require us to use valuation techniques to measure fair value that maximize the use of observable inputs and minimize the use of unobservable inputs. These inputs are prioritized as follows: Level 1 Unadjusted quoted prices in active markets for assets or liabilities identical to those to be reported at fair value Level 2 Other inputs that are observable directly or indirectly, such as quoted prices for similar assets or liabilities or market-corroborated inputs Level 3 Unobservable inputs for which there is little or no market data and which require us to develop our own assumptions about how market participants would price the assets or liabilities Assets and liabilities measured at fair value are based on the valuation techniques identified in the tables below. The valuation techniques are as follows: (a) Market approach. Prices and other relevant information generated by market transactions involving identical or comparable assets and liabilities; and (b) Income approach. Techniques to convert future amounts to a single current value based on market expectations (including present value techniques, option-pricing and excess earnings models).

Significant Accounting Polici_3

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Operating Revenue by Principal Geographic Region	The Company's operating revenue by principal geographic region (as defined by the U.S. Department of Transportation) for the years ended December 31 is presented in the table below (in millions): 2020 2019 2018 Domestic (U.S. and Canada) $ 9,911 $ 26,960 $ 25,552 Atlantic 2,226 7,387 7,103 Pacific 1,706 5,132 5,188 Latin America 1,512 3,780 3,460 Total $ 15,355 $ 43,259 $ 41,303
Roll Forward of Frequent Flyer Deferred Revenue	The table below presents a roll forward of Frequent flyer deferred revenue (in millions): Twelve Months Ended 2020 2019 Total Frequent flyer deferred revenue - beginning balance $ 5,276 $ 5,005 Total miles awarded 1,336 2,621 Travel miles redeemed (Passenger revenue) (568) (2,213) Non-travel miles redeemed (Other operating revenue) (69) (137) Total Frequent flyer deferred revenue - ending balance $ 5,975 $ 5,276
Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the consolidated balance sheets that sum to the total of the same such amounts shown in the statements of consolidated cash flows (in millions): UAL United At December 31, At December 31, 2020 2019 2018 2020 2019 2018 Current assets: Cash and cash equivalents $ 11,269 $ 2,762 $ 1,694 $ 11,269 $ 2,756 $ 1,688 Restricted cash 255 — — 255 — — Other assets: Restricted cash 218 106 105 218 106 105 Total cash, cash equivalents and restricted cash shown in the statement of consolidated cash flows $ 11,742 $ 2,868 $ 1,799 $ 11,742 $ 2,862 $ 1,793
Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the consolidated balance sheets that sum to the total of the same such amounts shown in the statements of consolidated cash flows (in millions): UAL United At December 31, At December 31, 2020 2019 2018 2020 2019 2018 Current assets: Cash and cash equivalents $ 11,269 $ 2,762 $ 1,694 $ 11,269 $ 2,756 $ 1,688 Restricted cash 255 — — 255 — — Other assets: Restricted cash 218 106 105 218 106 105 Total cash, cash equivalents and restricted cash shown in the statement of consolidated cash flows $ 11,742 $ 2,868 $ 1,799 $ 11,742 $ 2,862 $ 1,793
Estimated Useful Lives of Property and Equipment	The estimated useful lives of property and equipment are as follows: Estimated Useful Life (in years) Aircraft, spare engines and related rotable parts 25 to 30 Aircraft seats 10 to 15 Buildings 25 to 45 Other property and equipment 3 to 15 Computer software 5 to 15 Building improvements 1 to 40
Information about Goodwill and Other Intangible Assets	The following table presents information about the Company's goodwill and other intangible assets at December 31 (in millions): 2020 2019 Gross Accumulated Gross Accumulated Goodwill $ 4,527 $ 4,523 Indefinite-lived intangible assets Route authorities $ 1,020 $ 1,150 Airport slots 560 546 Tradenames and logos 593 593 Alliances 404 404 Total $ 2,577 $ 2,693 Finite-lived intangible assets Frequent flyer database $ 1,177 $ 971 $ 1,177 $ 931 Hubs 145 111 145 104 Contracts 120 116 120 111 Other 314 297 314 294 Total $ 1,756 $ 1,495 $ 1,756 $ 1,440

Earnings (Loss) Per Share (Tabl

Earnings (Loss) Per Share (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Computation of Earnings Per Share	The computations of UAL's basic and diluted earnings (loss) per share are set forth below for the years ended December 31 (in millions, except per share amounts): 2020 2019 2018 Earnings (loss) available to common stockholders $ (7,069) $ 3,009 $ 2,122 Basic weighted-average shares outstanding 279.4 258.8 275.5 Effect of share-based awards — 1.1 1.2 Diluted weighted-average shares outstanding 279.4 259.9 276.7 Earnings (loss) per share, basic $ (25.30) $ 11.63 $ 7.70 Earnings (loss) per share, diluted $ (25.30) $ 11.58 $ 7.67

Share-Based Compensation Plans

Share-Based Compensation Plans (Tables)	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Information Related to Share-Based Compensation Plan Cost	The following table provides information related to UAL's share-based compensation plan cost for the years ended December 31 (in millions): 2020 2019 2018 Compensation cost: RSUs $ 106 $ 98 $ 98 Restricted stock — 1 2 Stock options 2 1 1 Total $ 108 $ 100 $ 101
Summary of Unearned Compensation and Weighted-Average Remaining Period to Recognize Costs	The table below summarizes UAL's unearned compensation and weighted-average remaining period to recognize costs for all outstanding share-based awards that are probable of being achieved as of December 31, 2020 (in millions, except as noted): Unearned Compensation Weighted-Average RSUs $ 80 1.5 Stock options 8 4.6 Total $ 88
Summary of RSU and Restricted Stock Activity	The table below summarizes UAL's RSUs and restricted stock activity for the years ended December 31 (shares in millions): Liability Awards Equity Awards RSUs Weighted- Restricted Weighted- Outstanding at December 31, 2017 1.8 1.4 $ 63.99 0.3 $ 52.30 Granted 0.7 1.1 67.74 — — Vested (0.5) (0.5) 63.02 (0.2) 53.24 Forfeited (0.1) (0.2) 67.34 — — Outstanding at December 31, 2018 1.9 1.8 66.29 0.1 51.17 Granted 0.1 1.1 86.72 — — Vested (0.5) (0.8) 64.85 (0.1) 51.17 Forfeited (0.9) (0.1) 76.48 — — Outstanding at December 31, 2019 0.6 2.0 78.03 — — Granted 0.1 2.4 40.80 — — Vested (0.3) (0.8) 74.54 — — Forfeited — (0.4) 54.21 — — Outstanding at December 31, 2020 0.4 3.2 53.41 — —

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Components of AOCI	The tables below present the components of the Company's AOCI, net of tax (in millions): Pension and Investments and Other Deferred Taxes Total Balance at December 31, 2017 $ (1,102) $ (6) $ (39) $ (1,147) Change in value 377 (5) (83) 289 Amounts reclassified to earnings 62 (a) — (13) 49 Amounts reclassified to retained earnings ("RE") — 7 (b) (1) (b) 6 Balance at December 31, 2018 (663) (4) (136) (803) Change in value 105 7 (24) 88 Amounts reclassified to earnings (2) (a) (1) — (3) Balance at December 31, 2019 (560) 2 (160) (718) Change in value (993) — 221 (772) Amounts reclassified to earnings 451 (a) — (100) 351 Balance at December 31, 2020 $ (1,102) $ 2 $ (39) $ (1,139) (a) This AOCI component is included in the computation of net periodic pension and other postretirement costs. See Note 7 of this report for additional information on pensions and other postretirement liabilities. (b) These amounts represent the reclassification from AOCI to RE of the unrealized loss, and related tax, on the Company's investment in Azul Linhas Aéreas Brasileiras S.A. ("Azul") which was classified as an available-for-sale security prior to the Company adopting Accounting Standards Update No. 2016-01, Financial Instruments—Overall (Subtopic 825-10) effective January 1, 2018.

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Tax Provision (Benefit) Differed from Amounts Computed at the Statutory Federal Income Tax Rate and Significant Components	The income tax provision (benefit) differed from amounts computed at the statutory federal income tax rate and consisted of the following significant components (in millions) : UAL 2020 2019 2018 Income tax provision (benefit) at statutory rate $ (1,852) $ 822 $ 556 State income taxes, net of federal income tax benefit (110) 50 29 Foreign tax rate differential — (90) (84) Global intangible low-taxed income — 90 4 Foreign income taxes 1 1 2 Nondeductible employee meals 5 12 12 State rate change (2) — 3 Valuation allowance 197 (4) (3) Other, net 8 24 7 $ (1,753) $ 905 $ 526 Current $ (12) $ 23 $ 14 Deferred (1,741) 882 512 $ (1,753) $ 905 $ 526 United 2020 2019 2018 Income tax provision (benefit) at statutory rate $ (1,852) $ 822 $ 557 State income taxes, net of federal income tax (110) 50 29 Foreign tax rate differential — (90) (84) Global intangible low-taxed income — 90 4 Foreign income taxes 1 1 2 Nondeductible employee meals 5 12 12 State rate change (2) — 3 Valuation allowance 197 (4) (3) Other, net 8 24 7 $ (1,753) $ 905 $ 527 Current $ (12) $ 23 $ 14 Deferred (1,741) 882 513 $ (1,753) $ 905 $ 527
Temporary Differences and Carryforwards Giving Rise to Deferred Tax Assets and Liabilities	Temporary differences and carryforwards that give rise to deferred tax assets and liabilities at December 31, 2020 and 2019 were as follows (in millions): UAL United 2020 2019 2020 2019 Deferred income tax asset (liability): Federal and state net operating loss ("NOL") carryforwards $ 2,476 $ 695 $ 2,448 $ 668 Deferred revenue 1,409 1,287 1,409 1,287 Employee benefits, including pension, postretirement and medical 1,103 715 1,103 715 Operating lease liabilities 1,247 1,256 1,247 1,256 Sale leaseback liabilities 260 — 260 — Other 362 165 362 165 Less: Valuation allowance (247) (58) (247) (58) Total deferred tax assets $ 6,610 $ 4,060 $ 6,582 $ 4,033 Depreciation $ (4,789) $ (4,011) $ (4,789) $ (4,011) Operating lease right-of-use asset (1,028) (1,061) (1,028) (1,061) Intangibles (662) (724) (662) (724) Total deferred tax liabilities $ (6,479) $ (5,796) $ (6,479) $ (5,796) Net deferred tax asset (liability) $ 131 $ (1,736) $ 103 $ (1,763)

Pension and Other Postretirem_2

Pension and Other Postretirement Plans (Tables)	12 Months Ended
	Dec. 31, 2020
Retirement Benefits [Abstract]
Reconciliation of the Change in Benefit Obligation and Plan Assets and Funded Status	The following tables set forth the reconciliation of the beginning and ending balances of the benefit obligation and plan assets, the funded status and the amounts recognized in these financial statements for the defined benefit and other postretirement plans (in millions): Pension Benefits Year Ended December 31, 2020 Year Ended December 31, 2019 Accumulated benefit obligation: $ 5,387 $ 5,333 Change in projected benefit obligation: Projected benefit obligation at beginning of year $ 6,398 $ 5,396 Service cost 216 184 Interest cost 209 226 Actuarial loss 1,181 784 Special termination benefit 54 — Benefits paid (1,445) (200) Curtailment (105) — Other 17 8 Projected benefit obligation at end of year $ 6,525 $ 6,398 Change in plan assets: Fair value of plan assets at beginning of year $ 4,964 $ 3,827 Actual return on plan assets 521 684 Employer contributions 16 649 Benefits paid (1,445) (200) Other 13 4 Fair value of plan assets at end of year $ 4,069 $ 4,964 Funded status—Net amount recognized $ (2,456) $ (1,434) Pension Benefits December 31, 2020 December 31, 2019 Amounts recognized in the consolidated balance sheets consist of: Noncurrent asset $ 8 $ 14 Current liability (4) (2) Noncurrent liability (2,460) (1,446) Total liability $ (2,456) $ (1,434) Amounts recognized in accumulated other comprehensive loss consist of: Net actuarial loss $ (1,924) $ (1,652) Prior service cost (3) (4) Total accumulated other comprehensive loss $ (1,927) $ (1,656) Other Postretirement Benefits Year Ended December 31, 2020 Year Ended December 31, 2019 Change in benefit obligation: Benefit obligation at beginning of year $ 842 $ 1,391 Service cost 10 10 Interest cost 28 47 Plan participants' contributions 58 67 Benefits paid (164) (180) Actuarial loss 107 99 Plan amendments — (597) Special termination benefit 201 — Other — 5 Benefit obligation at end of year $ 1,082 $ 842 Change in plan assets: Fair value of plan assets at beginning of year $ 52 $ 53 Actual return on plan assets 1 1 Employer contributions 104 111 Plan participants' contributions 58 67 Benefits paid (164) (180) Fair value of plan assets at end of year 51 52 Funded status—Net amount recognized $ (1,031) $ (790)
Amounts Recognized in Consolidated Balance Sheet and Accumulated Other Comprehensive Income (Loss)	Other Postretirement Benefits Year Ended December 31, 2020 Year Ended December 31, 2019 Change in benefit obligation: Benefit obligation at beginning of year $ 842 $ 1,391 Service cost 10 10 Interest cost 28 47 Plan participants' contributions 58 67 Benefits paid (164) (180) Actuarial loss 107 99 Plan amendments — (597) Special termination benefit 201 — Other — 5 Benefit obligation at end of year $ 1,082 $ 842 Change in plan assets: Fair value of plan assets at beginning of year $ 52 $ 53 Actual return on plan assets 1 1 Employer contributions 104 111 Plan participants' contributions 58 67 Benefits paid (164) (180) Fair value of plan assets at end of year 51 52 Funded status—Net amount recognized $ (1,031) $ (790) Other Postretirement Benefits December 31, 2020 December 31, 2019 Amounts recognized in the consolidated balance sheets consist of: Current liability $ (37) $ (1) Noncurrent liability (994) (789) Total liability $ (1,031) $ (790) Amounts recognized in accumulated other comprehensive income consist of: Net actuarial gain $ 255 $ 403 Prior service credit 570 693 Total accumulated other comprehensive income $ 825 $ 1,096
Accumulated Benefit Obligation and Projected Benefit Obligation in Excess of Plan Assets	The following information relates to all pension plans with an accumulated benefit obligation and a projected benefit obligation in excess of plan assets at December 31 (in millions): 2020 2019 Projected benefit obligation $ 6,250 $ 6,161 Accumulated benefit obligation 5,163 5,137 Fair value of plan assets 3,786 4,714
Components Of Net Periodic Benefit Cost	Net periodic benefit cost for the years ended December 31 included the following components (in millions): 2020 2019 2018 Pension Benefits Other Postretirement Benefits Pension Benefits Other Postretirement Benefits Pension Benefits Other Postretirement Benefits Service cost $ 216 $ 10 $ 184 $ 10 $ 228 $ 12 Interest cost 209 28 226 47 217 61 Expected return on plan assets (328) (1) (291) (1) (292) (2) Amortization of unrecognized actuarial (gain) loss 162 (40) 118 (52) 130 (32) Amortization of prior service credits — (124) — (73) — (37) Settlement loss - VSPs 430 — — — — — Special termination benefit - VSPs 54 201 — — — — Curtailment 1 — — — — — Other 22 — 5 — 1 — Net periodic benefit cost (credit) $ 766 $ 74 $ 242 $ (69) $ 284 $ 2
Assumptions Used for Benefit Plans	The assumptions used for the benefit plans were as follows: Pension Benefits Assumptions used to determine benefit obligations 2020 2019 Discount rate 2.72 % 3.52 % Rate of compensation increase 3.88 % 3.89 % Assumptions used to determine net expense Discount rate 3.51 % 4.21 % Expected return on plan assets 7.31 % 7.40 % Rate of compensation increase 3.88 % 3.89 % Other Postretirement Benefits Assumptions used to determine benefit obligations 2020 2019 Discount rate 2.43 % 3.35 % Assumptions used to determine net expense Discount rate 3.35 % 4.30 % Expected return on plan assets 3.00 % 3.00 % Health care cost trend rate assumed for next year 5.80 % 6.00 % Rate to which the cost trend rate is assumed to decline (ultimate trend rate in 2033) 4.50 % 5.00 %
Allocation of Plan Assets	United's plan assets are allocated within the following guidelines: Percent of Total Expected Long-Term Equity securities 30-45 % 10 % Fixed-income securities 35-50 4 Alternatives 15-25 7
Pension and Other Postretirement Plan Assets	The following tables present information about United's pension and other postretirement plan assets at December 31 (in millions): 2020 2019 Pension Plan Assets: Total Level 1 Level 2 Level 3 Assets Measured at NAV(a) Total Level 1 Level 2 Level 3 Assets Measured at NAV(a) Equity securities funds $ 1,606 $ 55 $ 125 $ 96 $ 1,330 $ 1,957 $ 47 $ 117 $ 71 $ 1,722 Fixed-income securities 1,644 — 548 49 1,047 1,732 — 687 69 976 Alternatives 669 — — 195 474 776 — — 205 571 Other investments 150 132 8 10 — 499 466 21 12 — Total $ 4,069 $ 187 $ 681 $ 350 $ 2,851 $ 4,964 $ 513 $ 825 $ 357 $ 3,269 Other Postretirement Benefit Plan Assets: Deposit administration fund $ 51 $ — $ — $ 51 $ — $ 52 $ — $ — $ 52 $ — (a) In accordance with the relevant accounting standards, certain investments that are measured at fair value using the net asset value ("NAV") per share (or its equivalent) have not been classified in the fair value hierarchy. These investments are commingled funds that invest in fixed-income instruments including bonds, debt securities, and other similar instruments issued by various U.S. and non-U.S. public- or private-sector entities. Redemption periods for these investments range from daily to semiannually.
Defined Benefit Plan Assets Measured at Fair Value Using Unobservable Inputs	The reconciliation of United's benefit plan assets measured at fair value using unobservable inputs (Level 3) for the years ended December 31, 2020 and 2019 is as follows (in millions): 2020 2019 Balance at beginning of year $ 409 $ 350 Actual return (loss) on plan assets: Sold during the year 4 12 Held at year end 13 (1) Purchases, sales, issuances and settlements (net) (25) 48 Balance at end of year $ 401 $ 409
Estimated Future Benefit Payments	The estimated future benefit payments, net of expected participant contributions, in United's pension plans and other postretirement benefit plans as of December 31, 2020 are as follows (in millions): Pension Other Postretirement 2021 $ 325 $ 88 2022 339 118 2023 353 100 2024 351 87 2025 376 83 Years 2026 – 2030 2,113 359
Participation in the IAM National Pension Plan	United's participation in the IAM National Pension Plan ("IAM Plan") for the annual period ended December 31, 2020 is outlined in the table below. In addition to the additional required contributions described in table below, contributions in 2020 were affected by COVID-19 impacts on United's operations and consequently employee hours paid. The risks of participating in these multi-employer plans are different from single-employer plans, as United may be subject to additional risks that others do not meet their obligations, which in certain circumstances could revert to United. The IAM Plan reported $510 million in employers' contributions for the year ended December 31, 2019. For 2019, the Company's contributions to the IAM Plan represented more than 10% of total contributions to the IAM Plan. The 2020 information is not available as Form 5500 is not final for the plan year. Pension Fund IAM National Pension Fund ("Fund") EIN/ Pension Plan Number 51-6031295 — 002 Pension Protection Act Zone Status (2020 and 2019) Critical (2020) and Endangered (2019). A plan generally is in "endangered" status if its funded percentage is less than 80 percent. A plan is in "critical" status if the funded percentage is less than 65 percent. On April 17, 2019, the IAM National Pension Fund Board of Trustees voluntarily elected for the Fund to be in critical status effective for the plan year beginning January 1, 2019 to strengthen the Fund's financial health. FIP/RP Status Pending/Implemented A 10-year Rehabilitation Plan effective, January 1, 2022, was adopted on April 17, 2019 that requires the Company to make an additional contribution of 2.5% of the hourly contribution rate, compounded annually for the length of the Rehabilitation Plan, effective June 1, 2019. United's Contributions $53 million, $59 million and $52 million in the years ended December 31, 2020, 2019 and 2018, respectively Surcharge Imposed No Expiration Date of Collective Bargaining Agreement N/A

Investments and Fair Value Me_2

Investments and Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis	The table below presents disclosures about the fair value of financial assets and liabilities measured at fair value on a recurring basis in the Company's financial statements as of December 31 (in millions): 2020 2019 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Cash and cash equivalents $ 11,269 $ 11,269 $ — $ — $ 2,762 $ 2,762 $ — $ — Restricted cash - current (Note 1) 255 255 — — — — — — Restricted cash - non-current (Note 1) 218 218 — — 106 106 — — Short-term investments: Corporate debt 330 — 330 — 1,045 — 1,045 — Asset-backed securities 51 — 51 — 690 — 690 — U.S. government and agency notes 33 — 33 — 124 — 124 — Certificates of deposit placed through an account registry service — — — — 35 — 35 — Other fixed-income securities — — — — 95 — 95 — Other investments measured at NAV — — — — 193 — — — Long-term investments: Equity securities 205 205 — — 385 385 — — AVH Derivative Assets — — — — 24 — — 24 Other assets 36 — — 36 — — — —
Carrying Values and Estimated Fair Values of Financial Instruments	The table below presents the carrying values and estimated fair values of financial instruments not presented in the tables above as of December 31 (in millions). Carrying amounts include any related discounts, premiums and issuance costs: 2020 2019 Carrying Amount Fair Value Carrying Amount Fair Value Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Long-term debt $ 26,747 $ 27,441 $ — $ 21,985 $ 5,456 $ 14,552 $ 15,203 $ — $ 11,398 $ 3,805
Description of Fair Value of Financial Instruments and Fair Value Methodology	Fair value of the financial instruments included in the tables above was determined as follows: Description Fair Value Methodology Cash and cash equivalents The carrying amounts approximate fair value because of the short-term maturity of these assets. Short-term investments, other than Other investments measured at NAV, Fair value is based on (a) the trading prices of the investment or similar instruments, (b) an income approach, which uses valuation techniques to convert future amounts into a single present amount based on current market expectations about those future amounts when observable trading prices are not available, or (c) broker quotes obtained by third-party valuation services. Other investments measured at NAV In accordance with the relevant accounting standards, certain investments that are measured at fair value using the NAV per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in the table above are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the statement of financial position. The investments measured using NAV are shares of mutual funds that invest in fixed-income instruments including bonds, debt securities, and other similar instruments issued by various U.S. and non-U.S. public- or private-sector entities. The Company can redeem its shares at any time at NAV subject to a three-day settlement period. AVH Derivative Assets Fair values are calculated using a Monte Carlo simulation approach. Unobservable inputs include expected volatility, expected dividend yield and control and acquisition premiums. Other assets Fair value is determined utilizing the Black-Scholes options pricing model. Long-term debt Fair values were based on either market prices or the discounted amount of future cash flows using our current incremental rate of borrowing for similar liabilities or assets.

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Summary of Long-Term Debt	(In millions) Maturity Dates Interest Rate(s) at December 31, 2020 At December 31, 2020 2019 Secured Aircraft notes (a) 2021 — 2032 0.73 % — 9.80 % $ 14,538 $ 11,585 MileagePlus Senior Secured Notes 2027 6.50 % 3,800 — MileagePlus Term Loan Facility (a) 2027 5.49 % 3,000 — Revolving Credit Facility (a) 2022 1.49 % 1,000 — CARES Act Term Loan Facility (a) 2025 3.24 % 520 — Term Loan Facility (a) 2024 2.49 % 1,444 1,459 Unsecured Notes 2022 — 2025 4.25 % — 5.00 % 1,050 1,350 PSP Note 2030 1.00 % 1,501 — Other unsecured debt 2023 — 2029 4.00 % — 5.75 % 448 339 27,301 14,733 Less: unamortized debt discount, premiums and debt issuance costs (554) (181) Less: current portion of long-term debt (1,911) (1,407) Long-term debt, net $ 24,836 $ 13,145 (a) Financing includes variable rate debt based on LIBOR (or another index rate), generally subject to a floor, plus a specified margin ranging from 0.49% to 5.25%.
Contractual Principal Payments under Outstanding Long-Term Debt Agreements	The table below presents the Company's contractual principal payments (not including debt discount or debt issuance costs) at December 31, 2020 under then-outstanding long-term debt agreements in each of the next five calendar years (in millions): 2021 $ 1,911 2022 3,852 2023 2,699 2024 5,132 2025 3,739 After 2025 9,968 $ 27,301
Details of Pass Through Trusts	Certain details of the pass-through trusts with proceeds received from issuance of debt in 2020 are as follows (in millions, except stated interest rate): EETC Class Principal Final expected distribution date Stated interest rate Total proceeds received from issuance of debt during 2020 Total debt recorded September 2019 AA $ 702 May 2032 2.70% $ 189 $ 702 September 2019 A 287 May 2028 2.90% 77 287 September 2019 B 232 May 2028 3.50% 62 232 October 2020 A 3,000 October 2027 5.88% 3,000 3,000 February 2021 B 600 January 2026 4.88% — — $ 4,821 $ 3,328 $ 4,221
Summary of Collateral Covenants and Cross Default Provisions	The collateral, covenants and cross default provisions of the Company's principal debt instruments that contain such provisions are summarized in the table below: Debt Instrument Collateral, Covenants and Cross Default Provisions Various equipment notes and other notes payable Secured by certain aircraft, spare engines and spare parts. The indentures contain events of default that are customary for aircraft financings, including in certain cases cross default to other related aircraft. Credit Agreement Secured by certain of United's international route authorities, specified take-off and landing slots at certain airports and certain other assets. The Credit Agreement requires the Company to maintain at least $2.0 billion of unrestricted liquidity at all times, which includes unrestricted cash, short-term investments and any undrawn amounts under any revolving credit facility, and to maintain a minimum ratio of appraised value of collateral to the outstanding obligations under the Credit Agreement of 1.6 to 1.0 at all times. The Credit Agreement contains covenants that, among other things, restrict the ability of UAL and its restricted subsidiaries (as defined in the Credit Agreement) to make investments and to pay dividends on or repurchase stock. The Credit Agreement contains events of default customary for this type of financing, including a cross payment default and cross acceleration provision to certain other material indebtedness of the Company. CARES Act Credit Agreement Secured by liens on (i) certain route authorities of United and certain related slots and gate leaseholds and other related assets, (ii) certain aircraft and (iii) certain flight simulators and related assets. The CARES Act Credit Agreement requires the Company to maintain at least $2.0 billion of unrestricted liquidity at all times, which includes, among other things, unrestricted cash, certain short-term investments and any undrawn amounts under any revolving credit facility or under the CARES Act Credit Agreement, and to maintain a minimum ratio of appraised value of collateral to the outstanding obligations under the CARES Act Credit Agreement of 1.6 to 1.0. The CARES Act Credit Agreement contains covenants that, among other things, (i) restrict the ability of UAL and its subsidiaries to make investments and to pay dividends on or repurchase stock, (ii) require United to maintain certain levels of scheduled service and (iii) create certain limitations on executive compensation. The CARES Act Credit Agreement contains events of default customary for this type of financing, including a cross payment default and cross acceleration provision to certain other material indebtedness of the Company. MileagePlus Notes and Term Loan Facility Secured by first-priority security interests in substantially all of the assets of the Issuers, other than excluded property and subject to certain permitted liens, including security interests in specified cash accounts that include the accounts into which MileagePlus revenues are or will be paid by United's marketing partners and by United. PSP and PSP2 Notes The PSP Note and the PSP2 Note represent senior unsecured indebtedness of UAL. The PSP Note and the PSP2 Note are guaranteed by United. If any subsidiary of UAL (other than United) guarantees other unsecured indebtedness of UAL with a principal balance in excess of a specified amount, then such subsidiary shall be required to guarantee the obligations of UAL under the PSP Note and the PSP2 Note. Unsecured notes The indentures for these notes contain covenants that, among other things, restrict the ability of the Company and its restricted subsidiaries (as defined in the indentures) to incur additional indebtedness and pay dividends on or repurchase stock, although the Company currently has ample ability under these restrictions to repurchase stock under the Company's share repurchase programs.

Leases and Capacity Purchase _2

Leases and Capacity Purchase Agreements (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Components of Lease Cost	The Company's lease cost for the years ended December 31 included the following components (in millions): 2020 2019 2018 Operating lease cost $ 933 $ 1,038 $ 1,213 Variable and short-term lease cost 1,968 2,548 2,569 Amortization of finance lease assets 88 68 75 Interest on finance lease liabilities 16 85 44 Sublease income (23) (32) (38) Total lease cost $ 2,982 $ 3,707 $ 3,863
Summary of Scheduled Future Minimum Lease Payments under Operating Leases	The table below summarizes the Company's scheduled future minimum lease payments under operating and finance leases, recorded on the balance sheet, as of December 31, 2020 (in millions): Operating Leases Finance Leases 2021 $ 847 $ 198 2022 693 59 2023 723 51 2024 704 47 2025 585 35 After 2025 3,979 64 Minimum lease payments 7,531 454 Imputed interest (1,933) (48) Present value of minimum lease payments 5,598 406 Less: current maturities of lease obligations (612) (182) Long-term lease obligations $ 4,986 $ 224
Summary of Scheduled Future Minimum Lease Payments under Finance Leases	The table below summarizes the Company's scheduled future minimum lease payments under operating and finance leases, recorded on the balance sheet, as of December 31, 2020 (in millions): Operating Leases Finance Leases 2021 $ 847 $ 198 2022 693 59 2023 723 51 2024 704 47 2025 585 35 After 2025 3,979 64 Minimum lease payments 7,531 454 Imputed interest (1,933) (48) Present value of minimum lease payments 5,598 406 Less: current maturities of lease obligations (612) (182) Long-term lease obligations $ 4,986 $ 224
Additional Information Related to Leases	The table below presents additional information related to our leases as of December 31: 2020 2019 Weighted-average remaining lease term - operating leases 11 years 11 years Weighted-average remaining lease term - finance leases 4 years 6 years Weighted-average discount rate - operating leases 5.1 % 5.2 % Weighted-average discount rate - finance leases 4.4 % 5.7 %
Supplemental Cash Flow Information Related to Leases	The table below presents supplemental cash flow information related to leases during the year ended December 31 (in millions): 2020 2019 2018 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows for operating leases $ 788 $ 902 $ 1,078 Operating cash flows for finance leases 20 70 53 Financing cash flows for finance leases 66 151 79
Future Lease Payment Under Terms of Capacity Purchase Agreement	Based on these assumptions as of December 31, 2020, our future payments through the end of the terms of our CPAs are presented in the table below (in billions): 2021 $ 1.8 2022 1.8 2023 1.7 2024 1.5 2025 1.2 After 2025 3.1 $ 11.1

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Summary of Commitments to Purchase Aircraft	As of December 31, 2020 (adjusted to include the effects of the February 26, 2021 agreement with The Boeing Company ("Boeing") discussed below), United had firm commitments and options to purchase aircraft from Boeing, Airbus S.A.S. ("Airbus") and Embraer S.A. ("Embraer") presented in the table below: Scheduled Aircraft Deliveries Aircraft Type Number of Firm 2021 2022 After 2022 Airbus A321XLR 50 — — 50 Airbus A350 45 — — 45 Boeing 737 MAX 188 21 40 127 Boeing 787 11 11 — — Embraer E175 4 4 — — (a) United also has options and purchase rights for additional aircraft. The table below summarizes United's commitments as of December 31, 2020 (adjusted to include the effects of the February 26, 2021 agreement with Boeing), which include aircraft and related spare engines, aircraft improvements and all non-aircraft capital commitments (in billions): 2021 $ 4.9 2022 2.9 2023 2.8 2024 1.6 2025 2.0 After 2025 10.1 $ 24.3

Special Charges and Unrealize_2

Special Charges and Unrealized (Gains) Losses on Investments (Tables)	12 Months Ended
	Dec. 31, 2020
Restructuring and Related Activities [Abstract]
Components of Special Charges	Special charges and unrealized gains and losses on investments in the statements of consolidated operations consisted of the following for the years ended December 31 (in millions): Operating: 2020 2019 2018 CARES Act grant $ (3,536) $ — $ — Severance and benefit costs 575 16 41 Impairment of assets 318 171 377 Termination of an engine maintenance service agreement — — 64 (Gains) losses on sale of assets and other special charges 27 59 5 Total operating special charges (credit) (2,616) 246 487 Nonoperating credit loss on BRW Term Loan and related guarantee 697 — — Nonoperating special termination benefits and settlement losses 687 — — Nonoperating unrealized (gains) losses on investments 194 (153) 5 Total nonoperating special charges and unrealized (gains) losses on investments 1,578 (153) 5 Total operating and nonoperating special charges (credit) and unrealized (gains) losses on investments (1,038) 93 492 Income tax expense (benefit), net of valuation allowance 404 (21) (110) Income tax adjustments (Note 6) — — (5) Total operating and nonoperating special charges (credit) and unrealized (gains) losses on investments, net of income taxes $ (634) $ 72 $ 377

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Summary of Selected Quarterly Financial Data	Quarter Ended (In millions, except per share amounts) March 31 June 30 September 30 December 31 2020 Operating revenue $ 7,979 $ 1,475 $ 2,489 $ 3,412 Loss from operations (972) (1,637) (1,615) (2,135) Net loss (1,704) (1,627) (1,841) (1,897) Basic and diluted loss per share (6.86) (5.79) (6.33) (6.39) 2019 Operating revenue $ 9,589 $ 11,402 $ 11,380 $ 10,888 Income from operations 495 1,472 1,473 861 Net income 292 1,052 1,024 641 Basic earnings per share 1.09 4.03 4.01 2.54 Diluted earnings per share 1.09 4.02 3.99 2.53
Impact of Significant Items on Quarterly Results	UAL's quarterly financial data is subject to seasonal fluctuations and historically its second and third quarter financial results, which reflect higher travel demand, are better than its first and fourth quarter financial results. UAL's quarterly results were impacted by the following significant items (in millions): Quarter Ended March 31 June 30 September 30 December 31 2020 CARES Act grant $ — $ (1,589) $ (1,494) $ (453) Impairment of assets 50 80 51 137 Severance and benefit costs — 63 350 162 (Gains) losses on sale of assets and other special charges 13 (3) 12 5 Total operating special charges (credit) 63 (1,449) (1,081) (149) Nonoperating special termination benefits and settlement losses — 231 415 41 Nonoperating unrealized (gains) losses on investments 319 (9) (15) (101) Nonoperating credit loss on BRW Term Loan and related guarantee 697 — — — Total nonoperating special charges and unrealized (gains) losses on investments 1,016 222 400 (60) Total operating and nonoperating special charges (credit) and unrealized (gains) losses on investments 1,079 (1,227) (681) (209) Income tax expense (benefit), net of valuation allowance (14) 241 148 29 Total operating and nonoperating special charges (credit) and unrealized (gains) losses on investments, net of income taxes $ 1,065 $ (986) $ (533) $ (180) 2019 Impairment of assets $ 8 $ 61 $ — $ 102 Severance and benefit costs 6 6 2 2 (Gains) losses on sale of assets and other special charges 4 4 25 26 Total operating special charges 18 71 27 130 Nonoperating unrealized (gains) losses on investments (17) (34) (21) (81) Total special charges and unrealized (gains) losses on investments 1 37 6 49 Income tax benefit related to special charges and unrealized (gains) losses on investments — (8) (2) (11) Total special charges and unrealized (gains) losses on investments, net of income tax $ 1 $ 29 $ 4 $ 38

Overview (Details)

Overview (Details) employee in Thousands

Sep. 28, 2020USD ($)

Jul. 02, 2020USD ($)

Apr. 21, 2020USD ($)

Apr. 20, 2020USD ($)

Jul. 31, 2020employee

Feb. 25, 2021USD ($)

Mar. 31, 2021

Dec. 31, 2020USD ($)employee

Sep. 30, 2020USD ($)

Jun. 30, 2020USD ($)

Mar. 31, 2020USD ($)

Dec. 31, 2019USD ($)

Sep. 30, 2019USD ($)

Jun. 30, 2019USD ($)

Mar. 31, 2019USD ($)

Dec. 31, 2020USD ($)employee

Dec. 31, 2019USD ($)

Dec. 31, 2018USD ($)

Feb. 15, 2021USD ($)

Jan. 15, 2021USD ($)

Unusual or Infrequent Item, or Both [Line Items]

Net income (loss)

$ (1,897,000,000)

$ (1,841,000,000)

$ (1,627,000,000)

$ (1,704,000,000)

$ 641,000,000

$ 1,024,000,000

$ 1,052,000,000

$ 292,000,000

$ (7,069,000,000)

$ 3,009,000,000

$ 2,122,000,000

Percent of capacity cut

57.00%

Rolling cancellation period

60 days

Proceeds from issuance of debt

$ 16,044,000,000

1,847,000,000

1,594,000,000

Proceeds from the issuance of common stock

$ 1,100,000,000

2,100,000,000

Payroll taxes deferred under the CARES Act

$ 199,000,000

Number of employees notified of plans for workforce reduction | employee

36

Number of employee furloughs | employee

13

13

Number of employees subject to voluntary options | employee

9

9

Total funding provided under the Payroll Support Program

$ 5,100,000,000

Funding provided through direct grants under the Payroll Support Program

3,600,000,000

Funding provided through loans under the Payroll Support Program

$ 1,500,000,000

Cash received under the Payroll Support Program

$ 5,100,000,000

Subsequent Event

Unusual or Infrequent Item, or Both [Line Items]

Total funding provided under the Payroll Support Program

$ 2,600,000,000

Funding provided through direct grants under the Payroll Support Program

$ 1,900,000,000

Cash received under the Payroll Support Program

$ 1,300,000,000

Forecast

Unusual or Infrequent Item, or Both [Line Items]

Percent of capacity cut

51.00%

CARES Act Credit Agreement | Line of Credit

Unusual or Infrequent Item, or Both [Line Items]

Credit agreement

$ 7,500,000,000

7,500,000,000

Notes, Secured Term Loans and Aircraft Financing

Unusual or Infrequent Item, or Both [Line Items]

Proceeds from issuance of debt

$ 13,400,000,000

Unsecured Debt | PSP Note

Unusual or Infrequent Item, or Both [Line Items]

Term of debt

10 years

Unsecured Debt | PSP2 Note | Subsequent Event

Unusual or Infrequent Item, or Both [Line Items]

Funding provided through loans under the Payroll Support Program

$ 753,000,000

Term of debt

10 years

Line of Credit | CARES Act Credit Agreement

Unusual or Infrequent Item, or Both [Line Items]

Proceeds from issuance of debt

$ 520,000,000

Credit agreement

$ 7,500,000,000

CEO and President

Unusual or Infrequent Item, or Both [Line Items]

Voluntary pay reduction

100.00%

Non-Employee Directors

Unusual or Infrequent Item, or Both [Line Items]

Voluntary pay reduction

100.00%

United Airlines, Inc.

Unusual or Infrequent Item, or Both [Line Items]

Net income (loss)

$ (7,067,000,000)

3,011,000,000

2,123,000,000

Proceeds from issuance of debt

16,044,000,000

$ 1,847,000,000

$ 1,594,000,000

United Airlines, Inc. | Secured Debt | Revolving Credit Facility

Unusual or Infrequent Item, or Both [Line Items]

Proceeds from lines of credit

$ 1,000,000,000

1,000,000,000

Credit agreement

$ 2,000,000,000

$ 2,000,000,000

Significant Accounting Polici_4

Significant Accounting Policies - Operating Revenue by Principal Geographic Region (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Operating revenue	$ 3,412	$ 2,489	$ 1,475	$ 7,979	$ 10,888	$ 11,380	$ 11,402	$ 9,589	$ 15,355	$ 43,259	$ 41,303
Domestic (U.S. and Canada)
Disaggregation of Revenue [Line Items]
Operating revenue									9,911	26,960	25,552
Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue									2,226	7,387	7,103
Pacific
Disaggregation of Revenue [Line Items]
Operating revenue									1,706	5,132	5,188
Latin America
Disaggregation of Revenue [Line Items]
Operating revenue									$ 1,512	$ 3,780	$ 3,460

Significant Accounting Polici_5

Significant Accounting Policies - Narrative (Details) $ in Millions	Apr. 01, 2020	Mar. 31, 2020	Dec. 31, 2020USD ($)plane	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)		Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2020USD ($)planesegment	Dec. 31, 2019USD ($)		Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Jan. 01, 2020USD ($)
Summary Of Significant Accounting Policies [Line Items]
Expiration period for refundable tickets												1 year
Extended expiration period for refundable tickets												24 months
Percent of ETCs and FFCs with expiration dates extending beyond 12 months			74.00%									74.00%
Number of operating segments | segment												1
Revenue			$ 3,412	$ 2,489	$ 1,475	$ 7,979	$ 10,888		$ 11,380	$ 11,402	$ 9,589	$ 15,355	$ 43,259		$ 41,303
Excise taxes refunded to customers but still outstanding from the U.S. government			150									$ 150
Period over which miles are expected to be redeemed												two years
Cash collateral for a standby letter of credit			217									$ 217
Amounts to be used for the payment of fees, principal and interest			6,800									6,800
Carrying value of computer software			548				422					548	422
Amortization expense												55	60		67
Projected amortization expense in 2021			50									50
Projected amortization expense in 2022			40									40
Projected amortization expense in 2023			37									37
Projected amortization expense in 2024			32									32
Projected amortization expense in 2025			28									28
Advertising expense												$ 87	$ 212		211
Accounting Standards Update [Extensible List]												us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201613Member	[1]		us-gaap:AccountingStandardsUpdate201601Member
Stockholders' equity			$ 5,960				11,531					$ 5,960	$ 11,531		10,042	$ 8,788
Boeing 757-200
Summary Of Significant Accounting Policies [Line Items]
Number of planes permanently grounded | plane			11									11
Tangible asset impairment charges			$ 94
Retained Earnings
Summary Of Significant Accounting Policies [Line Items]
Stockholders' equity			2,626				9,716					$ 2,626	9,716		6,715	4,603
Adoption of New Accounting Standard
Summary Of Significant Accounting Policies [Line Items]
Stockholders' equity							(17)	[1]					(17)	[1]		0
Adoption of New Accounting Standard | Retained Earnings
Summary Of Significant Accounting Policies [Line Items]
Stockholders' equity							$ (17)	[1]					(17)	[1]		$ (6)	$ (17)
Minimum
Summary Of Significant Accounting Policies [Line Items]
Frequent flier program expiration period												1 year
Maximum
Summary Of Significant Accounting Policies [Line Items]
Frequent flier program expiration period												9 years
Computer software
Summary Of Significant Accounting Policies [Line Items]
Depreciation expense												$ 172	135		122
Advance Ticket Sales
Summary Of Significant Accounting Policies [Line Items]
Expiration period for advance ticket sales	24 months	12 months
Contract liabilities			$ 3,100									3,100
Revenue recognized												3,000	3,400		3,100
Ancillary Fees Recorded within Passenger Revenues
Summary Of Significant Accounting Policies [Line Items]
Revenue												918	2,400		2,200
Other Operating Revenue
Summary Of Significant Accounting Policies [Line Items]
Revenue												1,902	2,455		2,360
Other Operating Revenue | Chase and Other Partner Agreements
Summary Of Significant Accounting Policies [Line Items]
Revenue												$ 1,700	$ 2,000		2,000
One-time payment															$ 50
[1]	Transition adjustment due to the adoption of Accounting Standards Update No. 2016-13, Financial Instruments — Credit Losses

Significant Accounting Polici_6

Significant Accounting Policies - Roll Forward of Frequent Flier Deferred Revenue (Details) - Frequent Flyer - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Movement in Deferred Revenue [Roll Forward]
Total Frequent flyer deferred revenue - beginning balance	$ 5,276	$ 5,005
Total miles awarded	1,336	2,621
Travel miles redeemed (Passenger revenue)	(568)	(2,213)
Non-travel miles redeemed (Other operating revenue)	(69)	(137)
Total Frequent flyer deferred revenue - ending balance	$ 5,975	$ 5,276

Significant Accounting Polici_7

Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 11,269	$ 2,762	$ 1,694
Restricted cash	255	0	0
Other assets:
Restricted cash	218	106	105
Total cash, cash equivalents and restricted cash shown in the statement of consolidated cash flows	11,742	2,868	1,799	$ 1,591
United Airlines, Inc.
Current assets:
Cash and cash equivalents	11,269	2,756	1,688
Restricted cash	255	0	0
Other assets:
Restricted cash	218	106	105
Total cash, cash equivalents and restricted cash shown in the statement of consolidated cash flows	$ 11,742	$ 2,862	$ 1,793	$ 1,585

Significant Accounting Polici_8

Significant Accounting Policies - Estimated Useful Lives of Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2020
Aircraft, spare engines and related rotable parts | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	25 years
Aircraft, spare engines and related rotable parts | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	30 years
Aircraft seats | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	10 years
Aircraft seats | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	15 years
Buildings | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	25 years
Buildings | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	45 years
Other property and equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Other property and equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	15 years
Computer software | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Computer software | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	15 years
Building improvements | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	1 year
Building improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	40 years

Significant Accounting Polici_9

Significant Accounting Policies - Information about Goodwill and Other Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Goodwill	$ 4,527	$ 4,523
Indefinite-lived Intangible Assets [Line Items]
Gross  Carrying Amount	2,577	2,693
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,756	1,756
Accumulated Amortization	1,495	1,440
Route authorities
Indefinite-lived Intangible Assets [Line Items]
Gross  Carrying Amount	1,020	1,150
Airport slots and gates
Indefinite-lived Intangible Assets [Line Items]
Gross  Carrying Amount	560	546
Tradenames and logos
Indefinite-lived Intangible Assets [Line Items]
Gross  Carrying Amount	593	593
Alliances
Indefinite-lived Intangible Assets [Line Items]
Gross  Carrying Amount	404	404
Frequent flyer database
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,177	1,177
Accumulated Amortization	971	931
Hubs
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	145	145
Accumulated Amortization	111	104
Contracts
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	120	120
Accumulated Amortization	116	111
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	314	314
Accumulated Amortization	$ 297	$ 294

Common Stockholders' Equity a_2

Common Stockholders' Equity and Preferred Securities (Details) - USD ($)	Apr. 21, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 15, 2021	Sep. 28, 2020	Jun. 15, 2020	Apr. 20, 2020
Class of Stock [Line Items]
Number of shares repurchased (in shares)		4,000,000
Repurchases of common stock		$ 342,000,000	$ 1,641,000,000	$ 1,250,000,000
Common stock, par value (in dollars per share)		$ 0.01	$ 0.01
Proceeds from the issuance of common stock	$ 1,100,000,000	$ 2,100,000,000
Common stock reserved for future issuance (in shares)		6,000,000
Junior preferred stock outstanding (in shares)		2
Junior preferred stock par value per share (in dollars per share)		$ 0.01
Preferred stock authorized to issue (in shares)		250,000,000
Public Offering
Class of Stock [Line Items]
Sale of common stock (in shares)	43,000,000
Common stock, par value (in dollars per share)	$ 0.01						$ 0.01
Share price (in dollars per share)	$ 26.50
Equity Distribution Agreement
Class of Stock [Line Items]
Sale of common stock (in shares)		21,400,000
Share price (in dollars per share)		$ 46.70
Proceeds from the issuance of common stock		$ 989,000,000
Number of shares issuable under Equity Distribution Agreement (up to) (in shares)							28,000,000
CARES Act Credit Agreement | Line of Credit
Class of Stock [Line Items]
Aggregate principal amount						$ 520,000,000
PSP Warrants
Class of Stock [Line Items]
Number of warrants issuable under agreement (up to)								4,600,000
Number of warrants issuable under agreement (up to)		4,800,000						2,300,000
Strike price (in dollars per share)		$ 31.50
Term of warrants		5 years
Fair value of warrants outstanding		$ 66,000,000
Credit Agreement Warrants
Class of Stock [Line Items]
Number of warrants issuable under agreement (up to)						16,400,000
Number of warrants issuable under agreement (up to)						1,700,000
Strike price (in dollars per share)						$ 31.50
Term of warrants						5 years
Fair value of warrants outstanding						$ 30,000,000
Amount of warrants issued as a percent of the principal amount of disbursements						10.00%
PSP2 Warrants | Subsequent Event
Class of Stock [Line Items]
Number of warrants issuable under agreement (up to)					1,700,000
Strike price (in dollars per share)					$ 43.26
Term of warrants					5 years

Earnings (Loss) Per Share (Deta

Earnings (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Earnings (loss) available to common stockholders									$ (7,069)	$ 3,009	$ 2,122
Basic weighted-average shares outstanding (in shares)									279.4	258.8	275.5
Effect of share-based awards (in shares)									0	1.1	1.2
Diluted weighted-average shares outstanding (in shares)									279.4	259.9	276.7
Earnings per share, basic (in dollars per share)	$ (6.39)	$ (6.33)	$ (5.79)	$ (6.86)	$ 2.54	$ 4.01	$ 4.03	$ 1.09	$ (25.30)	$ 11.63	$ 7.70
Earnings per share, diluted (in dollars per share)					$ 2.53	$ 3.99	$ 4.02	$ 1.09	$ (25.30)	$ 11.58	$ 7.67

Share-Based Compensation Plan_2

Share-Based Compensation Plans - Narrative (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of RSUs and restricted stock vested in period	$ 87	$ 99	$ 70
Stock option awards outstanding (in shares)	700
Stock option awards exercisable (in shares)	300
Weighted-average exercise price of stock options outstanding (in dollars per share)	$ 82.12
Weighted-average exercise price of stock options exercisable (in dollars per share)	$ 58.25
Weighted average remaining contractual lives of stock options outstanding	6 years 3 months 18 days
Weighted average remaining contractual lives of stock options exercisable	3 years 6 months
Intrinsic value of stock options outstanding	$ 0
Intrinsic value of stock options exercisable	$ 0
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (in shares)	2,500
Number of days used to compute performance period average closing price of restricted stock units	20 days
Liabilities related to share based payments	$ 29
Payment related to share-based liabilities	$ 26	$ 41	$ 28
Time-Vested RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (in shares)	2,200
Vesting period	3 years
Performance-Based RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (in shares)	300
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares)	0	307	0
Percentage of premium of the grant date fair market value		25.00%
Weighted-average grant date exercise price of stock options granted (in dollars per share)		$ 110.21

Share-Based Compensation Plan_3

Share-Based Compensation Plans - Information Related to Share-Based Compensation Plan Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost	$ 108	$ 100	$ 101
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost	106	98	98
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost	0	1	2
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost	$ 2	$ 1	$ 1

Share-Based Compensation Plan_4

Share-Based Compensation Plans - Summary of Unearned Compensation and Weighted-Average Remaining Period to Recognize Costs (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unearned compensation	$ 88
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unearned compensation	$ 80
Weighted average remaining period	1 year 6 months
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unearned compensation	$ 8
Weighted average remaining period	4 years 7 months 6 days

Share-Based Compensation Plan_5

Share-Based Compensation Plans - Summary of RSU and Restricted Stock Activity (Details) - $ / shares shares in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Liability Awards - RSUs
Awards
Outstanding (in shares)	0.6	1.9	1.8
Granted (in shares)	0.1	0.1	0.7
Vested (in shares)	(0.3)	(0.5)	(0.5)
Forfeited (in shares)	0	(0.9)	(0.1)
Outstanding (in shares)	0.4	0.6	1.9
Equity Awards - RSUs
Awards
Outstanding (in shares)	2	1.8	1.4
Granted (in shares)	2.4	1.1	1.1
Vested (in shares)	(0.8)	(0.8)	(0.5)
Forfeited (in shares)	(0.4)	(0.1)	(0.2)
Outstanding (in shares)	3.2	2	1.8
Weighted- Average Grant Price
Outstanding (in dollars per share)	$ 78.03	$ 66.29	$ 63.99
Granted (in dollars per share)	40.80	86.72	67.74
Vested (in dollars per share)	74.54	64.85	63.02
Forfeited (in dollars per share)	54.21	76.48	67.34
Outstanding (in dollars per share)	$ 53.41	$ 78.03	$ 66.29
Restricted  Stock
Awards
Outstanding (in shares)	0	0.1	0.3
Granted (in shares)	0	0	0
Vested (in shares)	0	(0.1)	(0.2)
Forfeited (in shares)	0	0	0
Outstanding (in shares)	0	0	0.1
Weighted- Average Grant Price
Outstanding (in dollars per share)	$ 0	$ 51.17	$ 52.30
Granted (in dollars per share)	0	0	0
Vested (in dollars per share)	0	51.17	53.24
Forfeited (in dollars per share)	0	0	0
Outstanding (in dollars per share)	$ 0	$ 0	$ 51.17

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) - Components of the Company's AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, deferred taxes	$ (160)	$ (136)	$ (39)
Balance	11,531	10,042	8,788
Change in value, deferred tax	221	(24)	(83)
Change in value	(772)	88	289
Amounts reclassified to earnings, deferred taxes	(100)	0	(13)
Amounts reclassified to earnings	351	(3)	49
Amounts reclassified to retained earnings, deferred taxes			(1)
Amounts reclassified to retained earnings			6
Balance, deferred taxes	(39)	(160)	(136)
Balance	5,960	11,531	10,042
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(718)	(803)	(1,147)
Balance	(1,139)	(718)	(803)
Pension and Other Postretirement Liabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, before tax	(560)	(663)	(1,102)
Change in value, before tax	(993)	105	377
Amounts reclassified to earnings, before tax	451	(2)	62
Amounts reclassified to retained earnings, before tax			0
Balance, before tax	(1,102)	(560)	(663)
Investments and Other
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, before tax	2	(4)	(6)
Change in value, before tax	0	7	(5)
Amounts reclassified to earnings, before tax	0	(1)	0
Amounts reclassified to retained earnings, before tax			7
Balance, before tax	$ 2	$ 2	$ (4)

Income Taxes - Income Tax Provi

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, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
Income tax provision (benefit) at statutory rate	$ (1,852)	$ 822	$ 556
State income taxes, net of federal income tax benefit	(110)	50	29
Foreign tax rate differential	0	(90)	(84)
Global intangible low-taxed income	0	90	4
Foreign income taxes	1	1	2
Nondeductible employee meals	5	12	12
State rate change	(2)	0	3
Valuation allowance	197	(4)	(3)
Other, net	8	24	7
Income tax expense (benefit)	(1,753)	905	526
Current	(12)	23	14
Deferred	(1,741)	882	512
United Airlines, Inc.
Income Taxes [Line Items]
Income tax provision (benefit) at statutory rate	(1,852)	822	557
State income taxes, net of federal income tax benefit	(110)	50	29
Foreign tax rate differential	0	(90)	(84)
Global intangible low-taxed income	0	90	4
Foreign income taxes	1	1	2
Nondeductible employee meals	5	12	12
State rate change	(2)	0	3
Valuation allowance	197	(4)	(3)
Other, net	8	24	7
Income tax expense (benefit)	(1,753)	905	527
Current	(12)	23	14
Deferred	$ (1,741)	$ 882	$ 513

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
Valuation allowance	$ 197	$ (4)	$ (3)
Unrecognized tax benefits	57	53	39
Unrecognized tax benefits that would impact effective tax rate if recognized	57
Capital loss carryforwards, valuation allowance	185
United Airlines, Inc.
Income Taxes [Line Items]
Valuation allowance	197	$ (4)	$ (3)
Federal
Income Taxes [Line Items]
Tax credits	42
Federal | United Airlines, Inc.
Income Taxes [Line Items]
NOL carryforwards	11,000
Tax effected amount of NOLs	2,300
NOLs without an expiration date	$ 9,400
Federal | Minimum
Income Taxes [Line Items]
Tax credit expiration period	1 year
Federal | Maximum
Income Taxes [Line Items]
Tax credit expiration period	18 years
Federal | 2026 | United Airlines, Inc.
Income Taxes [Line Items]
NOL carryforwards	$ 100
Federal | 2028 | United Airlines, Inc.
Income Taxes [Line Items]
NOL carryforwards	500
Federal | 2029 | United Airlines, Inc.
Income Taxes [Line Items]
NOL carryforwards	400
Federal | 2032 | United Airlines, Inc.
Income Taxes [Line Items]
NOL carryforwards	200
Federal | 2033 | United Airlines, Inc.
Income Taxes [Line Items]
NOL carryforwards	400
State
Income Taxes [Line Items]
Tax credits	33
NOL and tax credit carryforwards, valuation allowance	62
State | United Airlines, Inc.
Income Taxes [Line Items]
NOL carryforwards	3,700
Tax effected amount of NOLs	$ 200
State | Minimum
Income Taxes [Line Items]
Tax credit expiration period	1 year
State | Minimum | United Airlines, Inc.
Income Taxes [Line Items]
NOL expiration period	5 years
State | Maximum
Income Taxes [Line Items]
Tax credit expiration period	11 years
State | Maximum | United Airlines, Inc.
Income Taxes [Line Items]
NOL expiration period	20 years

Income Taxes - Temporary Differ

Income Taxes - Temporary Differences and Carryforwards Giving Rise to Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred income tax asset (liability):
Federal and state net operating loss ("NOL") carryforwards	$ 2,476	$ 695
Deferred revenue	1,409	1,287
Employee benefits, including pension, postretirement and medical	1,103	715
Operating lease liabilities	1,247	1,256
Sale leaseback liabilities	260	0
Other	362	165
Less: Valuation allowance	(247)	(58)
Total deferred tax assets	6,610	4,060
Depreciation	(4,789)	(4,011)
Operating lease right-of-use asset	(1,028)	(1,061)
Intangibles	(662)	(724)
Total deferred tax liabilities	(6,479)	(5,796)
Net deferred tax asset	131
Net deferred tax asset (liability)		(1,736)
United Airlines, Inc.
Deferred income tax asset (liability):
Federal and state net operating loss ("NOL") carryforwards	2,448	668
Deferred revenue	1,409	1,287
Employee benefits, including pension, postretirement and medical	1,103	715
Operating lease liabilities	1,247	1,256
Sale leaseback liabilities	260	0
Other	362	165
Less: Valuation allowance	(247)	(58)
Total deferred tax assets	6,582	4,033
Depreciation	(4,789)	(4,011)
Operating lease right-of-use asset	(1,028)	(1,061)
Intangibles	(662)	(724)
Total deferred tax liabilities	(6,479)	(5,796)
Net deferred tax asset	$ 103
Net deferred tax asset (liability)		$ (1,763)

Pension and Other Postretirem_3

Pension and Other Postretirement Plans - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans And Defined Contribution Plans Disclosures [Line Items]
Profit sharing and payroll tax expense	$ 0	$ 491	$ 334
Minimum
Defined Benefit Plans And Defined Contribution Plans Disclosures [Line Items]
Percentage of pre-tax earnings paid for profit sharing plan	5.00%
Maximum
Defined Benefit Plans And Defined Contribution Plans Disclosures [Line Items]
Percentage of pre-tax earnings paid for profit sharing plan	20.00%
IAM National Pension Plan
Defined Benefit Plans And Defined Contribution Plans Disclosures [Line Items]
Multi-employer plan contributions		$ 510
Percent of company's contribution to plan		10.00%
United Airlines, Inc.
Defined Benefit Plans And Defined Contribution Plans Disclosures [Line Items]
Expense for defined contribution plans	$ 687	$ 735	693
United Airlines, Inc. | Minimum
Defined Benefit Plans And Defined Contribution Plans Disclosures [Line Items]
Employer contribution percentage	1.00%
United Airlines, Inc. | Maximum
Defined Benefit Plans And Defined Contribution Plans Disclosures [Line Items]
Employer contribution percentage	16.00%
Pension Benefits
Defined Benefit Plans And Defined Contribution Plans Disclosures [Line Items]
Charges for special termination benefits under VSPs	$ 54	0	0
Payments for defined benefit plan settlements	1,400
Settlement losses	430
Increase in postretirement benefit liability if there was a 50 basis point decrease in the weighted average discount rate	800
Increase in benefits expense if there was a 50 basis point decrease in the weighted average discount rate	78
Decrease in expected long-term rate of return on plan assets if there was a 50 basis point decrease in the weighted average discount rate	25
Other Postretirement Benefits
Defined Benefit Plans And Defined Contribution Plans Disclosures [Line Items]
Charges for special termination benefits under VSPs	201	$ 0	$ 0
Increase in postretirement benefit liability if there was a 50 basis point decrease in the weighted average discount rate	48
Increase in benefits expense if there was a 50 basis point decrease in the weighted average discount rate	2
Expected employer contributions to pension and postretirement plans	$ 82

Pension and Other Postretirem_4

Pension and Other Postretirement Plans - Reconciliation of the Change in Benefit Obligation and Plan Asset, Funded Status and Amounts Recognized in the Financial Statements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Amounts recognized in the consolidated balance sheets consist of:
Total liability	$ (2,456)	$ (1,434)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	5,387	5,333
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	6,398	5,396
Service cost	216	184	$ 228
Interest cost	209	226	217
Benefits paid	(1,445)	(200)
Actuarial loss	1,181	784
Special termination benefit	54	0
Benefits paid	(1,445)	(200)
Curtailment	(105)	0
Other	17	8
Projected benefit obligation at end of year	6,525	6,398	5,396
Change in plan assets:
Fair value of plan assets at beginning of year	4,964	3,827
Actual return on plan assets	521	684
Employer contributions	16	649
Benefits paid	(1,445)	(200)
Other	13	4
Fair value of plan assets at end of year	4,069	4,964	3,827
Funded status—Net amount recognized	(2,456)	(1,434)
Amounts recognized in the consolidated balance sheets consist of:
Noncurrent asset	8	14
Current liability	(4)	(2)
Noncurrent liability	(2,460)	(1,446)
Amounts recognized in accumulated other comprehensive loss consist of:
Net actuarial loss	(1,924)	(1,652)
Prior service cost	(3)	(4)
Total accumulated other comprehensive loss	(1,927)	(1,656)
Other Postretirement Benefits
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	842	1,391
Service cost	10	10	12
Interest cost	28	47	61
Plan participants' contributions	58	67
Benefits paid	(164)	(180)
Actuarial loss	107	99
Plan amendments	0	(597)
Special termination benefit	201	0
Benefits paid	(164)	(180)
Other	0	5
Projected benefit obligation at end of year	1,082	842	1,391
Change in plan assets:
Fair value of plan assets at beginning of year	52	53
Actual return on plan assets	1	1
Employer contributions	104	111
Plan participants' contributions	58	67
Benefits paid	(164)	(180)
Fair value of plan assets at end of year	51	52	$ 53
Funded status—Net amount recognized	(1,031)	(790)
Amounts recognized in the consolidated balance sheets consist of:
Current liability	(37)	(1)
Noncurrent liability	(994)	(789)
Total liability	(1,031)	(790)
Amounts recognized in accumulated other comprehensive loss consist of:
Net actuarial loss	(255)	(403)
Prior service cost	(570)	(693)
Total accumulated other comprehensive loss	$ (825)	$ (1,096)

Pension and Other Postretirem_5

Pension and Other Postretirement Plans - Accumulated Benefit Obligation and Projected Benefit Obligation in Excess of Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Retirement Benefits [Abstract]
Projected benefit obligation	$ 6,250	$ 6,161
Accumulated benefit obligation	5,163	5,137
Fair value of plan assets	$ 3,786	$ 4,714

Pension and Other Postretirem_6

Pension and Other Postretirement Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 216	$ 184	$ 228
Interest cost	209	226	217
Expected return on plan assets	(328)	(291)	(292)
Amortization of unrecognized actuarial (gain) loss	162	118	130
Amortization of prior service credits	0	0	0
Settlement loss - VSPs	430	0	0
Special termination benefit - VSPs	54	0	0
Curtailment	1	0	0
Other	(22)	(5)	(1)
Net periodic benefit cost (credit)	766	242	284
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	10	10	12
Interest cost	28	47	61
Expected return on plan assets	(1)	(1)	(2)
Amortization of unrecognized actuarial (gain) loss	(40)	(52)	(32)
Amortization of prior service credits	(124)	(73)	(37)
Settlement loss - VSPs	0	0	0
Special termination benefit - VSPs	201	0	0
Curtailment	0	0	0
Other	0	0	0
Net periodic benefit cost (credit)	$ 74	$ (69)	$ 2

Pension and Other Postretirem_7

Pension and Other Postretirement Plans - Assumptions Used for Benefit Plans (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Pension Benefits
Assumptions used to determine benefit obligations
Discount rate	2.72%	3.52%
Rate of compensation increase	3.88%	3.89%
Assumptions used to determine net expense
Discount rate	3.51%	4.21%
Expected return on plan assets	7.31%	7.40%
Rate of compensation increase	3.88%	3.89%
Other Postretirement Benefits
Assumptions used to determine benefit obligations
Discount rate	2.43%	3.35%
Assumptions used to determine net expense
Discount rate	3.35%	4.30%
Expected return on plan assets	3.00%	3.00%
Health care cost trend rate assumed for next year	5.80%	6.00%
Rate to which the cost trend rate is assumed to decline (ultimate trend rate in 2033)	4.50%	5.00%

Pension and Other Postretirem_8

Pension and Other Postretirement Plans - Allocation of Plan Assets (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return	3.00%	3.00%
Deposit Administration Fund | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Percent of total	100.00%
United Airlines, Inc. | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return	10.00%
United Airlines, Inc. | Equity securities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Percent of total	30.00%
United Airlines, Inc. | Equity securities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Percent of total	45.00%
United Airlines, Inc. | Fixed-income securities
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return	4.00%
United Airlines, Inc. | Fixed-income securities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Percent of total	35.00%
United Airlines, Inc. | Fixed-income securities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Percent of total	50.00%
United Airlines, Inc. | Alternatives
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return	7.00%
United Airlines, Inc. | Alternatives | Minimum
Defined Benefit Plan Disclosure [Line Items]
Percent of total	15.00%
United Airlines, Inc. | Alternatives | Maximum
Defined Benefit Plan Disclosure [Line Items]
Percent of total	25.00%

Pension and Other Postretirem_9

Pension and Other Postretirement Plans - Pension and Other Postretirement Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Level 3
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	$ 401	$ 409	$ 350
Pension Benefits
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	4,069	4,964	3,827
Pension Benefits | Level 1
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	187	513
Pension Benefits | Level 2
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	681	825
Pension Benefits | Level 3
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	350	357
Pension Benefits | Assets Measured at NAV
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	2,851	3,269
Pension Benefits | Equity securities funds
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	1,606	1,957
Pension Benefits | Equity securities funds | Level 1
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	55	47
Pension Benefits | Equity securities funds | Level 2
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	125	117
Pension Benefits | Equity securities funds | Level 3
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	96	71
Pension Benefits | Equity securities funds | Assets Measured at NAV
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	1,330	1,722
Pension Benefits | Fixed-income securities
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	1,644	1,732
Pension Benefits | Fixed-income securities | Level 1
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | Fixed-income securities | Level 2
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	548	687
Pension Benefits | Fixed-income securities | Level 3
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	49	69
Pension Benefits | Fixed-income securities | Assets Measured at NAV
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	1,047	976
Pension Benefits | Alternatives
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	669	776
Pension Benefits | Alternatives | Level 1
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | Alternatives | Level 2
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | Alternatives | Level 3
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	195	205
Pension Benefits | Alternatives | Assets Measured at NAV
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	474	571
Pension Benefits | Other investments
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	150	499
Pension Benefits | Other investments | Level 1
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	132	466
Pension Benefits | Other investments | Level 2
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	8	21
Pension Benefits | Other investments | Level 3
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	10	12
Pension Benefits | Other investments | Assets Measured at NAV
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	51	52	$ 53
Other Postretirement Benefits | Deposit administration fund
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	51	52
Other Postretirement Benefits | Deposit administration fund | Level 1
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits | Deposit administration fund | Level 2
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits | Deposit administration fund | Level 3
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	51	52
Other Postretirement Benefits | Deposit administration fund | Assets Measured at NAV
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0

Pension and Other Postretire_10

Pension and Other Postretirement Plans - Defined Benefit Plan Assets Measured at Fair Value Using Unobservable Inputs (Details) - Level 3 - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of year	$ 409	$ 350
Actual return (loss) on plan assets:
Sold during the year	4	12
Held at year end	13	(1)
Purchases, sales, issuances and settlements (net)	(25)	48
Fair value of plan assets at end of year	$ 401	$ 409

Pension and Other Postretire_11

Pension and Other Postretirement Plans - Estimated Future Benefit Payments (Details) $ in Millions	Dec. 31, 2020USD ($)
Pension Benefits
Pension and Other Postretirement
2021	$ 325
2022	339
2023	353
2024	351
2025	376
Years 2026 – 2030	2,113
Other Postretirement Benefits
Pension and Other Postretirement
2021	88
2022	118
2023	100
2024	87
2025	83
Years 2026 – 2030	$ 359

Pension and Other Postretire_12

Pension and Other Postretirement Plans - Participation in the IAM National Pension Plan (Details) - IAM National Pension Plan - Pension Benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Multiemployer Plans [Line Items]
Plan length	10 years
Additional contribution as a percentage of the hourly contribution rate	0.025%
Surcharge imposed	No
United Airlines, Inc.
Multiemployer Plans [Line Items]
Contributions	$ 53	$ 59	$ 52

Notes Receivable (Details)

Notes Receivable (Details) shares in Millions, adr in Millions	1 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2020USD ($)	Oct. 31, 2020USD ($)	Jan. 01, 2020USD ($)	Nov. 30, 2018USD ($)adrshares
BRW | Term Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan amount					$ 456,000,000
Number of shares pledged as collateral (in shares) | shares					516
Implied value equivalent of shares pledged as collateral (in ADRs) | adr					64.5
Carrying amount of loan receivable				$ 515,000,000
AVH | Convertible Term Loan | United Airlines, Inc. and Kingsland International Group, S.A.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest rate	3.00%
AVH | Convertible Term Loan | United Airlines, Inc.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Issuance of notes receivable	$ 150,000,000
AVH | DIP Loan | United Airlines, Inc.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest rate			14.50%
Notes receivable			$ 159,000,000
Other Notes Receivable Counterparties
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying amount of loan receivable		$ 31,000,000

Investments and Fair Value Me_3

Investments and Fair Value Measurements - Fair Value of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Measured on a Recurring Basis - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 11,269	$ 2,762
Restricted cash - current	255	0
Restricted cash - non-current	218	106
Equity securities	205	385
AVH Derivative Assets	0	24
Other assets	36	0
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	11,269	2,762
Restricted cash - current	255	0
Restricted cash - non-current	218	106
Equity securities	205	385
AVH Derivative Assets	0	0
Other assets	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Restricted cash - current	0	0
Restricted cash - non-current	0	0
Equity securities	0	0
AVH Derivative Assets	0	0
Other assets	0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Restricted cash - current	0	0
Restricted cash - non-current	0	0
Equity securities	0	0
AVH Derivative Assets	0	24
Other assets	36	0
Corporate debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	330	1,045
Corporate debt | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Corporate debt | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	330	1,045
Corporate debt | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	51	690
Asset-backed securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Asset-backed securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	51	690
Asset-backed securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
U.S. government and agency notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	33	124
U.S. government and agency notes | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
U.S. government and agency notes | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	33	124
U.S. government and agency notes | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Certificates of deposit placed through an account registry service
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	35
Certificates of deposit placed through an account registry service | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Certificates of deposit placed through an account registry service | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	35
Certificates of deposit placed through an account registry service | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Other fixed-income securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	95
Other fixed-income securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Other fixed-income securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	95
Other fixed-income securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Other investments measured at NAV
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	193
Other investments measured at NAV | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Other investments measured at NAV | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Other investments measured at NAV | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 0	$ 0

Investments and Fair Value Me_4

Investments and Fair Value Measurements - Narrative (Details) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2020USD ($)aircraft	Dec. 31, 2019USD ($)
Fair Value [Line Items]
Unrealized gain (loss) on derivative asset		$ (24)	$ 13
Investments in securities accounted for under the equity method		$ 139
Republic
Fair Value [Line Items]
Number of regional aircraft | aircraft		66
Champlain
Fair Value [Line Items]
Number of regional aircraft | aircraft		49
Asset-backed Securities | Minimum
Fair Value [Line Items]
Available-for-sale securities remaining maturities		1 year
Asset-backed Securities | Maximum
Fair Value [Line Items]
Available-for-sale securities remaining maturities		14 years
Corporate Debt
Fair Value [Line Items]
Available-for-sale securities remaining maturities		2 years
U.S. Government and Other Securities
Fair Value [Line Items]
Available-for-sale securities remaining maturities		1 year
Azul
Fair Value [Line Items]
Equity stake		2.00%
Gain (loss) on equity securities	$ (136)	$ 180
Carrying value of investment		$ 205
Azul | Preferred Stock
Fair Value [Line Items]
Equity stake		8.00%
Republic
Fair Value [Line Items]
Ownership stake		19.00%
ManaAir
Fair Value [Line Items]
Ownership stake		49.90%
Champlain
Fair Value [Line Items]
Ownership stake		40.00%
Fulcrum
Fair Value [Line Items]
Ownership interest		0.06
Carrying value of other investment		$ 51
Fulcrum | Preferred Stock
Fair Value [Line Items]
Ownership interest		0.07
CLEAR
Fair Value [Line Items]
Ownership interest		0.01
Carrying value of other investment		$ 9

Investments and Fair Value Me_5

Investments and Fair Value Measurements - Carrying Amounts and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, carrying amount	$ 26,747	$ 14,552
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	27,441	15,203
Fair Value | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Fair Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	21,985	11,398
Fair Value | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	$ 5,456	$ 3,805

Debt - Summary of Long-Term Deb

Debt - Summary of Long-Term Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Jul. 02, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long term debt	$ 27,301		$ 14,733
Less: unamortized debt discount, premiums and debt issuance costs	(554)		(181)
Less: current portion of long-term debt	(1,911)		(1,407)
Long-term debt, net	24,836		13,145
Secured | Revolving Credit Facility
Debt Instrument [Line Items]
Long term debt	$ 1,000		0
Fixed interest rate	1.49%
Secured | Revolving Credit Facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	0.49%
Secured | Revolving Credit Facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	5.25%
Secured | Aircraft notes
Debt Instrument [Line Items]
Long term debt	$ 14,538		11,585
Secured | Aircraft notes | Minimum
Debt Instrument [Line Items]
Fixed interest rate	0.73%
Secured | Aircraft notes | Maximum
Debt Instrument [Line Items]
Fixed interest rate	9.80%
Secured | Aircraft notes | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	0.49%
Secured | Aircraft notes | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	5.25%
Secured | MileagePlus Senior Secured Notes
Debt Instrument [Line Items]
Long term debt	$ 3,800		0
Fixed interest rate	6.50%	6.50%
Secured | MileagePlus Term Loan Facility
Debt Instrument [Line Items]
Long term debt	$ 3,000		0
Fixed interest rate	5.49%
Secured | MileagePlus Term Loan Facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	0.49%
Secured | MileagePlus Term Loan Facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	5.25%
Secured | CARES Act Term Loan Facility
Debt Instrument [Line Items]
Long term debt	$ 520		0
Fixed interest rate	3.24%
Secured | CARES Act Term Loan Facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	0.49%
Secured | CARES Act Term Loan Facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	5.25%
Secured | Term loan
Debt Instrument [Line Items]
Long term debt	$ 1,444		1,459
Fixed interest rate	2.49%
Secured | Term loan | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	0.49%
Secured | Term loan | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	5.25%
Unsecured | Notes
Debt Instrument [Line Items]
Long term debt	$ 1,050		1,350
Unsecured | Notes | Minimum
Debt Instrument [Line Items]
Fixed interest rate	4.25%
Unsecured | Notes | Maximum
Debt Instrument [Line Items]
Fixed interest rate	5.00%
Unsecured | PSP Note
Debt Instrument [Line Items]
Long term debt	$ 1,501		0
Fixed interest rate	1.00%
Unsecured | Other unsecured debt
Debt Instrument [Line Items]
Long term debt	$ 448		$ 339
Unsecured | Other unsecured debt | Minimum
Debt Instrument [Line Items]
Fixed interest rate	4.00%
Unsecured | Other unsecured debt | Maximum
Debt Instrument [Line Items]
Fixed interest rate	5.75%

Debt - Contractual Principal Pa

Debt - Contractual Principal Payments under Outstanding Long-Term Debt Agreements (Details) - UAL and United $ in Millions	Dec. 31, 2020USD ($)
Debt Instrument [Line Items]
2021	$ 1,911
2022	3,852
2023	2,699
2024	5,132
2025	3,739
After 2025	9,968
Long-term debt	$ 27,301

Debt - Narrative (Details)

Debt - Narrative (Details) - USD ($)

Sep. 28, 2020

Jul. 02, 2020

Apr. 20, 2020

Feb. 25, 2021

Dec. 31, 2020

Dec. 31, 2020

Dec. 31, 2019

Dec. 31, 2018

Feb. 15, 2021

Jan. 15, 2021

Jun. 30, 2020

Apr. 07, 2020

Mar. 20, 2020

Mar. 09, 2020

Debt Instrument [Line Items]

Total funding provided under the Payroll Support Program

$ 5,100,000,000

Funding provided through loans under the Payroll Support Program

$ 1,500,000,000

Proceeds from issuance of debt

$ 16,044,000,000

$ 1,847,000,000

$ 1,594,000,000

Long term debt

$ 27,301,000,000

27,301,000,000

14,733,000,000

Subsequent Event

Debt Instrument [Line Items]

Total funding provided under the Payroll Support Program

$ 2,600,000,000

United Airlines, Inc.

Debt Instrument [Line Items]

Proceeds from issuance of debt

$ 16,044,000,000

1,847,000,000

$ 1,594,000,000

Secured Debt | Revolving Credit Facility

Debt Instrument [Line Items]

Fixed interest rate

1.49%

1.49%

Long term debt

$ 1,000,000,000

$ 1,000,000,000

0

Secured Debt | Revolving Credit Facility | United Airlines, Inc.

Debt Instrument [Line Items]

Credit agreement

2,000,000,000

2,000,000,000

Available under revolving credit facility

$ 1,000,000,000

1,000,000,000

Proceeds from lines of credit

$ 1,000,000,000

$ 1,000,000,000

Secured Debt | LIBOR | Revolving Credit Facility | United Airlines, Inc.

Debt Instrument [Line Items]

Basis spread on variable rate

2.25%

Variable rate floor

0.00%

Secured Debt | Alternative Rate Based on Certain Market Interest Rates | Revolving Credit Facility | United Airlines, Inc.

Debt Instrument [Line Items]

Basis spread on variable rate

1.25%

Line of Credit | Revolving Credit Facility

Debt Instrument [Line Items]

Commitment fee percentage

0.75%

Line of Credit | Revolving Credit Facility | United Airlines, Inc.

Debt Instrument [Line Items]

Available under revolving credit facility

$ 1,000,000,000

PSP Note | Unsecured Debt

Debt Instrument [Line Items]

Term of debt

10 years

Fixed interest rate

1.00%

1.00%

Long term debt

$ 1,501,000,000

$ 1,501,000,000

0

PSP Note | Unsecured Debt | Years One through Five

Debt Instrument [Line Items]

Fixed interest rate

1.00%

1.00%

PSP Note | Unsecured Debt | Years Six through Ten | SOFR

Debt Instrument [Line Items]

Basis spread on variable rate

2.00%

Mileage Plus Senior Secured Notes | Secured Debt

Debt Instrument [Line Items]

Aggregate principal amount

$ 3,800,000,000

Fixed interest rate

6.50%

6.50%

6.50%

Long term debt

$ 3,800,000,000

$ 3,800,000,000

0

MileagePlus Term Loan Facility | Secured Debt

Debt Instrument [Line Items]

Fixed interest rate

5.49%

5.49%

Long term debt

$ 3,000,000,000

$ 3,000,000,000

0

MileagePlus Term Loan Facility | Line of Credit

Debt Instrument [Line Items]

Aggregate principal amount

$ 3,000,000,000

Proceeds from issuance of debt

$ 3,000,000,000

MileagePlus Term Loan Facility | Line of Credit | LIBOR

Debt Instrument [Line Items]

Basis spread on variable rate

5.25%

Variable rate floor

1.00%

CARES Act Credit Agreement | Line of Credit

Debt Instrument [Line Items]

Aggregate principal amount

$ 520,000,000

Proceeds from issuance of debt

520,000,000

Credit agreement

$ 7,500,000,000

CARES Act Credit Agreement | Line of Credit | LIBOR

Debt Instrument [Line Items]

Basis spread on variable rate

3.00%

Variable rate floor

0.00%

Used Aircraft Facility | Secured Debt

Debt Instrument [Line Items]

Aggregate principal amount

$ 2,000,000,000

Long term debt

14,538,000,000

14,538,000,000

$ 11,585,000,000

Spare Parts Facility | Secured Debt

Debt Instrument [Line Items]

Aggregate principal amount

$ 500,000,000

Spare Engines Facility | Secured Debt

Debt Instrument [Line Items]

Aggregate principal amount

$ 250,000,000

Term Loan Credit and Guaranty Agreement | Bridge Loan

Debt Instrument [Line Items]

Aggregate principal amount

$ 200,000,000

Pass-Through Certificates

Debt Instrument [Line Items]

Long term debt

12,100,000,000

12,100,000,000

Borrowings Financing Aircraft Purchases | Secured Debt

Debt Instrument [Line Items]

Aggregate principal amount

691,000,000

691,000,000

Special Facility Revenue Bonds | Secured Debt

Debt Instrument [Line Items]

Aggregate principal amount

$ 295,000,000

$ 295,000,000

Fixed interest rate

4.00%

4.00%

Special Facility Revenue Bonds | Mortgage

Debt Instrument [Line Items]

Long term debt

$ 159,000,000

$ 159,000,000

PSP2 Note | Unsecured Debt | Subsequent Event

Debt Instrument [Line Items]

Funding provided through loans under the Payroll Support Program

$ 753,000,000

Term of debt

10 years

Increase in principal amount as a percent of treasury disbursements

30.00%

PSP2 Note | Unsecured Debt | Years One through Five | Subsequent Event

Debt Instrument [Line Items]

Fixed interest rate

1.00%

PSP2 Note | Unsecured Debt | Years Six through Ten | SOFR | Subsequent Event

Debt Instrument [Line Items]

Basis spread on variable rate

2.00%

Debt - Details of Pass Through

Debt - Details of Pass Through Trusts (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Mar. 01, 2021	Feb. 28, 2021
Debt Instrument [Line Items]
Proceeds received from issuance of debt	$ 16,044,000,000	$ 1,847,000,000	$ 1,594,000,000
Total debt recorded	27,301,000,000	$ 14,733,000,000
Pass-Through Certificates
Debt Instrument [Line Items]
Proceeds received from issuance of debt	3,328,000,000
Total debt recorded	4,221,000,000
Pass-Through Certificates | Subsequent Event
Debt Instrument [Line Items]
Principal				$ 4,821,000,000
Class AA EETC - Issued September 2019 | Pass-Through Certificates
Debt Instrument [Line Items]
Principal	$ 702,000,000
Stated interest rate	2.70%
Proceeds received from issuance of debt	$ 189,000,000
Total debt recorded	702,000,000
Class A EETC - Issued September 2019 | Pass-Through Certificates
Debt Instrument [Line Items]
Principal	$ 287,000,000
Stated interest rate	2.90%
Proceeds received from issuance of debt	$ 77,000,000
Total debt recorded	287,000,000
Class B EETC - Issued September 2019 | Pass-Through Certificates
Debt Instrument [Line Items]
Principal	$ 232,000,000
Stated interest rate	3.50%
Proceeds received from issuance of debt	$ 62,000,000
Total debt recorded	232,000,000
Class A EETC - Issued October 2020 | Pass-Through Certificates
Debt Instrument [Line Items]
Principal	$ 3,000,000,000
Stated interest rate	5.88%
Proceeds received from issuance of debt	$ 3,000,000,000
Total debt recorded	$ 3,000,000,000
Class B EETC - Issued February 2021 | Pass-Through Certificates
Debt Instrument [Line Items]
Stated interest rate	4.88%
Total debt recorded	$ 0
Class B EETC - Issued February 2021 | Pass-Through Certificates | Subsequent Event
Debt Instrument [Line Items]
Principal					$ 600,000,000

Debt - Summary of Collateral Co

Debt - Summary of Collateral Covenants and Cross Default Provisions (Details) - Line of Credit $ in Billions	Dec. 31, 2020USD ($)
Credit Agreement
Debt Instrument [Line Items]
Unrestricted liquidity required for credit agreement	$ 2
Minimum ratio of appraised value of collateral for Credit Agreement	1.6
CARES Act Credit Agreement
Debt Instrument [Line Items]
Unrestricted liquidity required for credit agreement	$ 2
Minimum ratio of appraised value of collateral for Credit Agreement	1.6

Leases and Capacity Purchase _3

Leases and Capacity Purchase Agreements - Components of Lease Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease cost	$ 933	$ 1,038	$ 1,213
Variable and short-term lease cost	1,968	2,548	2,569
Amortization of finance lease assets	88	68	75
Interest on finance lease liabilities	16	85	44
Sublease income	(23)	(32)	(38)
Total lease cost	$ 2,982	$ 3,707	$ 3,863

Leases and Capacity Purchase _4

Leases and Capacity Purchase Agreements - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)aircraft	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Lessee, Lease, Description [Line Items]
Additional leases that have not yet commenced | $		$ 740
Lease terms of additional leases that have not yet commenced (up to)		12 years
Number of aircraft included in flight equipment		11
Number of aircraft qualified for sale recorded as operating lease right-of-use assets and current/long-term obligations		4
Boeing 787-9 and Boeing 737 MAX
Lessee, Lease, Description [Line Items]
Number of aircraft delivered under sale and leaseback transaction		15
United Airlines, Inc. | Cash Collateralized Letters of Credit
Lessee, Lease, Description [Line Items]
Number of regional aircraft		475
Mainline Aircraft
Lessee, Lease, Description [Line Items]
Number of aircraft subject to operating leases		104
Number of aircraft subject to finance leases		37
Regional Aircraft
Lessee, Lease, Description [Line Items]
Number of aircraft subject to operating leases		290
Number of aircraft subject to finance leases		45
Regional Aircraft | United Airlines, Inc. | Capacity Purchase Agreements
Lessee, Lease, Description [Line Items]
Expenses | $		$ 600	$ 1,000	$ 1,000
Accounts payable | $		$ 68	$ 69
Minimum | Mainline Aircraft
Lessee, Lease, Description [Line Items]
Initial term of operating leases		1 month
Minimum | Non-Aircraft
Lessee, Lease, Description [Line Items]
Initial term of operating leases		1 month
Maximum | Mainline Aircraft
Lessee, Lease, Description [Line Items]
Initial term of operating leases		12 years
Maximum | Non-Aircraft
Lessee, Lease, Description [Line Items]
Initial term of operating leases		32 years
Forecast | Capacity Purchase Agreements
Lessee, Lease, Description [Line Items]
Scheduled block hours increase (decrease) percentage	10.00%
Change in cash obligation | $	$ 85

Leases and Capacity Purchase _5

Leases and Capacity Purchase Agreements - Summary of Scheduled Future Minimum Lease Payments under Operating and Finance Leases (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Operating Leases
2021	$ 847
2022	693
2023	723
2024	704
2025	585
After 2025	3,979
Minimum lease payments	7,531
Imputed interest	(1,933)
Present value of minimum lease payments	5,598
Less: current maturities of lease obligations	(612)	$ (686)
Long-term lease obligations	4,986	4,946
Finance Leases
2021	198
2022	59
2023	51
2024	47
2025	35
After 2025	64
Minimum lease payments	454
Imputed interest	(48)
Present value of minimum lease payments	406
Less: current maturities of lease obligations	(182)	(46)
Long-term lease obligations	$ 224	$ 220

Leases and Capacity Purchase _6

Leases and Capacity Purchase Agreements - Additional Information Related to Leases (Details)	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Weighted-average remaining lease term - operating leases	11 years	11 years
Weighted-average remaining lease term - finance leases	4 years	6 years
Weighted-average discount rate - operating leases	5.10%	5.20%
Weighted-average discount rate - finance leases	4.40%	5.70%

Leases and Capacity Purchase _7

Leases and Capacity Purchase Agreements - Supplemental Cash Flow Information Related to Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows for operating leases	$ 788	$ 902	$ 1,078
Operating cash flows for finance leases	20	70	53
Financing cash flows for finance leases	$ 66	$ 151	$ 79

Leases and Capacity Purchase _8

Leases and Capacity Purchase Agreements - Future Lease Payment under Terms of Capacity Purchase Agreement (Details) $ in Billions	Dec. 31, 2020USD ($)
Leases [Abstract]
2021	$ 1.8
2022	1.8
2023	1.7
2024	1.5
2025	1.2
After 2025	3.1
Total	$ 11.1

Variable Interest Entities ("_2

Variable Interest Entities ("VIE") (Details) $ in Billions	Dec. 31, 2020USD ($)
Tax-Exempt Special Facilities Revenue Bonds
Variable Interest Entity [Line Items]
Underlying debt and interest	$ 1.9

Commitments and Contingencies -

Commitments and Contingencies - Firm Commitments and Options to Purchase Aircraft (Details)	Dec. 31, 2020aircraftCommitmentaircraft
Airbus A321XLR
Long-term Purchase Commitment [Line Items]
Number of firm commitments | aircraftCommitment	50
Scheduled aircraft deliveries in 2021	0
Scheduled aircraft deliveries in 2022	0
Scheduled aircraft deliveries after 2022	50
Airbus A350
Long-term Purchase Commitment [Line Items]
Number of firm commitments | aircraftCommitment	45
Scheduled aircraft deliveries in 2021	0
Scheduled aircraft deliveries in 2022	0
Scheduled aircraft deliveries after 2022	45
Boeing 737 MAX
Long-term Purchase Commitment [Line Items]
Number of firm commitments | aircraftCommitment	188
Scheduled aircraft deliveries in 2021	21
Scheduled aircraft deliveries in 2022	40
Scheduled aircraft deliveries after 2022	127
Boeing 787
Long-term Purchase Commitment [Line Items]
Number of firm commitments | aircraftCommitment	11
Scheduled aircraft deliveries in 2021	11
Scheduled aircraft deliveries in 2022	0
Scheduled aircraft deliveries after 2022	0
Embraer E175
Long-term Purchase Commitment [Line Items]
Number of firm commitments | aircraftCommitment	4
Scheduled aircraft deliveries in 2021	4
Scheduled aircraft deliveries in 2022	0
Scheduled aircraft deliveries after 2022	0

Commitments and Contingencies_2

Commitments and Contingencies - Narrative (Details)	12 Months Ended
	Dec. 31, 2020USD ($)aircraftCommitmentemployeeoption$ / sharesshares	Feb. 26, 2021aircraft	Nov. 30, 2020USD ($)
Commitments and Contingencies [Line Items]
Cash collateral for a standby letter of credit	$ 217,000,000
Aggregate balance	$ 11,100,000,000
Number of call options to purchase regional jet aircraft | option	303
United Airlines, Inc.
Commitments and Contingencies [Line Items]
Number of employees | employee	74,400
Percentage of employees represented by various U.S. labor organizations	84.00%
United Airlines, Inc. | Surety Bonds
Commitments and Contingencies [Line Items]
Long-term line of credit	$ 380,000,000
Tax-Exempt Special Facilities Revenue Bonds
Commitments and Contingencies [Line Items]
Guarantor obligations, maximum exposure	1,900,000,000
Tax-Exempt Special Facilities Revenue Bonds | Indirect Guarantee of Indebtedness
Commitments and Contingencies [Line Items]
Guarantor obligations, maximum exposure	293,000,000
Contingent liabilities based on participation	2,300,000,000
Aircraft Mortgage Debt
Commitments and Contingencies [Line Items]
Guarantor obligations, maximum exposure	119,000,000
Floating Rate Debt
Commitments and Contingencies [Line Items]
Aggregate principal amount	$ 9,800,000,000
Debt instrument, remaining terms	12 years
Loans And Leases From Non U S Entities
Commitments and Contingencies [Line Items]
Debt instrument, remaining terms	12 years
Aggregate balance	$ 8,300,000,000
Kingsland
Commitments and Contingencies [Line Items]
Number of shares that may be put to United (in shares) | shares	144,800,000
Number of ADRs that may be put to United (in shares) | shares	18,100,000
Market price of common stock at fifth anniversary (in dollars per share) | $ / shares	$ 12
Aggregate maximum possible combined put payment and guarantee amount	$ 217,000,000
Kingsland | Standby Letter of Credit
Commitments and Contingencies [Line Items]
Cash collateral for a standby letter of credit			$ 217,000,000
Boeing 737-700
Commitments and Contingencies [Line Items]
Number of firm commitments | aircraftCommitment	11
Airbus A319
Commitments and Contingencies [Line Items]
Number of firm commitments | aircraftCommitment	17
Boeing 737 MAX
Commitments and Contingencies [Line Items]
Number of firm commitments | aircraftCommitment	188
Boeing 737 MAX | Subsequent Event
Commitments and Contingencies [Line Items]
Scheduled aircraft deliveries for 2023 from new firm orders | aircraft		25
Scheduled aircraft deliveries for 2022 from rescheduled deliveries | aircraft		40
Scheduled aircraft deliveries for 2023 from rescheduled deliveries | aircraft		5

Commitments and Contingencies_3

Commitments and Contingencies - Summary of Commitments Related to the Acquisition of Aircraft (Details) $ in Billions	Dec. 31, 2020USD ($)
Commitments and Contingencies Disclosure [Abstract]
2021	$ 4.9
2022	2.9
2023	2.8
2024	1.6
2025	2
After 2025	10.1
Total	$ 24.3

Special Charges and Unrealize_3

Special Charges and Unrealized (Gains) Losses on Investments - Components of Special Charges (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating:
CARES Act grant	$ (453,000)	$ (1,494,000)	$ (1,589,000)	$ 0					$ (3,536,000)	$ 0	$ 0
Severance and benefit costs	162,000	350,000	63,000	0	$ 2,000	$ 2,000	$ 6,000	$ 6,000	575,000	16,000	41,000
Impairment of assets	137,000	51,000	80,000	50,000	102,000	0	61,000	8,000	318,000	171,000	377,000
Termination of an engine maintenance service agreement									0	0	64,000
(Gains) losses on sale of assets and other special charges	5,000	12,000	(3,000)	13,000	26,000	25,000	4,000	4,000	27,000	59,000	5,000
Total operating special charges (credit)	(149,000)	(1,081,000)	(1,449,000)	63,000	130,000	27,000	71,000	18,000	(2,616,000)	246,000	487,000
Nonoperating credit loss on BRW Term Loan and related guarantee	0	0	0	697,000					697,000	0	0
Nonoperating special termination benefits and settlement losses	41,000	415,000	231,000	0					687,000	0	0
Nonoperating unrealized (gains) losses on investments	(101,000)	(15,000)	(9,000)	319,000	(81,000)	(21,000)	(34,000)	(17,000)	194,000	(153,000)	5,000
Total special charges and unrealized (gains) losses on investments	(60,000)	400,000	222,000	1,016,000	49,000	6,000	37,000	1,000	1,578,000	(153,000)	5,000
Total operating and nonoperating special charges (credit) and unrealized (gains) losses on investments	(209,000)	(681,000)	(1,227,000)	1,079,000					(1,038,000)	93,000	492,000
Income tax expense (benefit), net of valuation allowance	29,000	148,000	241,000	(14,000)	(11,000)	(2,000)	(8,000)	0	404,000	(21,000)	(110,000)
Income tax adjustments									0	0	(5,000)
Total operating and nonoperating special charges (credit) and unrealized (gains) losses on investments, net of income taxes	$ (180,000)	$ (533,000)	$ (986,000)	$ 1,065,000	$ 38,000	$ 4,000	$ 29,000	$ 1,000	$ (634,000)	$ 72,000	$ 377,000

Special Charges and Unrealize_4

Special Charges and Unrealized (Gains) Losses on Investments - Narrative (Details)	1 Months Ended		3 Months Ended									12 Months Ended
	Jul. 31, 2020employee	May 31, 2018USD ($)	Dec. 31, 2020USD ($)employeeplane	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Mar. 31, 2017USD ($)employee	Dec. 31, 2020USD ($)employeeplane	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Special Charges [Line Items]
Cash received under the Payroll Support Program												$ 5,100,000,000
Cash received from grants												3,600,000,000
Proceeds from the issuance of an unsecured loan												1,500,000,000
Proceeds from issuance of warrants												66,000,000
Portion of grant recognized as a credit to special charges			$ 453,000,000	$ 1,494,000,000	$ 1,589,000,000	$ 0						$ 3,536,000,000	$ 0	$ 0
Number of employees notified of plans for workforce reduction | employee	36,000
Number of employee furloughs | employee			13,000									13,000
Number of employees subject to voluntary options | employee			9,000									9,000
Severance and benefit expenses			$ 162,000,000	350,000,000	63,000,000	0	$ 2,000,000	$ 2,000,000	$ 6,000,000	$ 6,000,000		$ 575,000,000	16,000,000	41,000,000
Impairment of right-of-use assets												38,000,000
Impairments related to cancelled projects												56,000,000
Settlement losses related to defined benefit pension plans			41,000,000	415,000,000	231,000,000	0						687,000,000	0	0
Nonoperating unrealized (gains) losses on investments			(101,000,000)	(15,000,000)	(9,000,000)	319,000,000	(81,000,000)	$ (21,000,000)	$ (34,000,000)	$ (17,000,000)		194,000,000	(153,000,000)	5,000,000
Unrealized loss on derivative assets												24,000,000	(13,000,000)
Expected credit loss allowance recorded			0	$ 0	$ 0	$ 697,000,000						697,000,000	0	0
Write-off of unexercised aircraft purchase													18,000,000
Other miscellaneous impairments													20,000,000
Charges related to contract terminations													25,000,000
Charges for the settlement of certain legal matters													18,000,000
Costs related to the transition of fleet types													14,000,000
Other charges													2,000,000
Gain (loss) on change in market value of equity investments														28,000,000
Gain (loss) due to the change in fair value of derivatives													13,000,000
Fair value adjustments related to aircraft purchased off lease, write-off of unexercised aircraft purchase options and other impairments														66,000,000
One-time termination charge related to engine maintenance service agreements												0	0	64,000,000
Losses due to the change in fair value of derivatives														(33,000,000)
COVID-19 [Member]
Special Charges [Line Items]
Portion of grant recognized as a credit to special charges												3,500,000,000
International Brotherhood of Teamsters
Special Charges [Line Items]
Severance and benefit expenses													2,000,000	22,000,000
International Brotherhood of Teamsters | Voluntary Early Out Program
Special Charges [Line Items]
Number of technicians and related employees electing to voluntarily separate from the Company | employee											1,000
Severance payment per participant											$ 100,000
Management
Special Charges [Line Items]
Severance and benefit expenses													14,000,000	19,000,000
Aircraft Engines
Special Charges [Line Items]
Tangible asset impairment charges													43,000,000
Hong Kong Routes
Special Charges [Line Items]
Intangible assets impairment charges													90,000,000	$ 206,000,000
Brazil Routes
Special Charges [Line Items]
Intangible assets impairment charges		$ 105,000,000
Azul
Special Charges [Line Items]
Gain (loss) on equity securities							$ 136,000,000					(180,000,000)
Gain (loss) on change in market value of equity investments													$ 140,000,000
Investments Excluding AVH Derivative Assets
Special Charges [Line Items]
Nonoperating unrealized (gains) losses on investments												$ 170,000,000
Boeing 757-200
Special Charges [Line Items]
Tangible asset impairment charges			$ 94,000,000
Number of planes permanently grounded | plane			11									11
Routes
Special Charges [Line Items]
Intangible assets impairment charges												$ 130,000,000

Selected Quarterly Financial _3

Selected Quarterly Financial Data (Unaudited) - Summary of Selected Quarterly FInancial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Operating revenue	$ 3,412	$ 2,489	$ 1,475	$ 7,979	$ 10,888	$ 11,380	$ 11,402	$ 9,589	$ 15,355	$ 43,259	$ 41,303
Loss from operations	(2,135)	(1,615)	(1,637)	(972)	861	1,473	1,472	495	(6,359)	4,301	3,229
Net income (loss)	$ (1,897)	$ (1,841)	$ (1,627)	$ (1,704)	$ 641	$ 1,024	$ 1,052	$ 292	$ (7,069)	$ 3,009	$ 2,122
Earnings per share, basic (in dollars per share)	$ (6.39)	$ (6.33)	$ (5.79)	$ (6.86)	$ 2.54	$ 4.01	$ 4.03	$ 1.09	$ (25.30)	$ 11.63	$ 7.70
Earnings per share, diluted (in dollars per share)					$ 2.53	$ 3.99	$ 4.02	$ 1.09	$ (25.30)	$ 11.58	$ 7.67

Selected Quarterly Financial _4

Selected Quarterly Financial Data (Unaudited) - Impact of Significant Items on Quarterly Results (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
CARES Act grant	$ (453,000)	$ (1,494,000)	$ (1,589,000)	$ 0					$ (3,536,000)	$ 0	$ 0
Impairment of assets	137,000	51,000	80,000	50,000	$ 102,000	$ 0	$ 61,000	$ 8,000	318,000	171,000	377,000
Severance and benefit costs	162,000	350,000	63,000	0	2,000	2,000	6,000	6,000	575,000	16,000	41,000
(Gains) losses on sale of assets and other special charges	5,000	12,000	(3,000)	13,000	26,000	25,000	4,000	4,000	27,000	59,000	5,000
Total operating special charges (credit)	(149,000)	(1,081,000)	(1,449,000)	63,000	130,000	27,000	71,000	18,000	(2,616,000)	246,000	487,000
Nonoperating special termination benefits and settlement losses	41,000	415,000	231,000	0					687,000	0	0
Nonoperating unrealized (gains) losses on investments	(101,000)	(15,000)	(9,000)	319,000	(81,000)	(21,000)	(34,000)	(17,000)	194,000	(153,000)	5,000
Nonoperating credit loss on BRW Term Loan and related guarantee	0	0	0	697,000					697,000	0	0
Total special charges and unrealized (gains) losses on investments	(60,000)	400,000	222,000	1,016,000	49,000	6,000	37,000	1,000	1,578,000	(153,000)	5,000
Total operating and nonoperating special charges (credit) and unrealized (gains) losses on investments	(209,000)	(681,000)	(1,227,000)	1,079,000					(1,038,000)	93,000	492,000
Income tax expense (benefit), net of valuation allowance	29,000	148,000	241,000	(14,000)	(11,000)	(2,000)	(8,000)	0	404,000	(21,000)	(110,000)
Total operating and nonoperating special charges (credit) and unrealized (gains) losses on investments, net of income taxes	$ (180,000)	$ (533,000)	$ (986,000)	$ 1,065,000	$ 38,000	$ 4,000	$ 29,000	$ 1,000	$ (634,000)	$ 72,000	$ 377,000

Schedule II - Valuation and Q_2

Schedule II - Valuation and Qualifying Accounts (Details) - UAL and United - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for doubtful accounts
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$ 9	$ 8	$ 7
Additions Charged to Costs and Expenses	70	17	17
Deductions	16	16	16
Other	15	0	0
Balance at End of Period	78	9	8
Obsolescence allowance-spare parts
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	425	412	354
Additions Charged to Costs and Expenses	88	76	73
Deductions	35	63	15
Other	0	0	0
Balance at End of Period	478	425	412
Allowance for credit losses - notes receivable
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	0
Additions Charged to Costs and Expenses	518
Deductions	0
Other	4
Balance at End of Period	522	0
Valuation allowance for deferred tax assets
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	58	59	63
Additions Charged to Costs and Expenses	197	0	2
Deductions	8	1	6
Other	0	0	0
Balance at End of Period	$ 247	$ 58	$ 59