Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Receivables, allowance for doubtful accounts	$ 7	$ 10
Aircraft fuel, spare parts and supplies, obsolescence allowance	354	295
Intangibles, accumulated amortization	$ 1,313	$ 1,234
Common stock, par value	$ 0.01	$ 0.01
Common shares, authorized	1,000,000,000	1,000,000,000
Common shares, outstanding	286,973,195	314,612,744
United Airlines, Inc.
Receivables, allowance for doubtful accounts	$ 7	$ 10
Aircraft fuel, spare parts and supplies, obsolescence allowance	354	295
Intangibles, accumulated amortization	$ 1,313	$ 1,234
Common stock, par value	$ 0.01	$ 0.01
Common shares, authorized	1,000	1,000
Common shares, issued	1,000	1,000
Common shares, outstanding	1,000	1,000