Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Allowance for doubtful accounts	$ 9	$ 8
Obsolescence allowance for aircraft fuel, spare parts and supplies	387	412
Accumulated amortization on intangibles	$ 1,410	$ 1,380
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)	257,729,166	269,914,769
United Airlines, Inc.
Allowance for doubtful accounts	$ 9	$ 8
Obsolescence allowance for aircraft fuel, spare parts and supplies	387	412
Accumulated amortization on intangibles	$ 1,410	$ 1,380
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