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