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