Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Receivables, allowance for doubtful accounts	$ 20	$ 13
Aircraft fuel, spare parts and supplies, obsolescence allowance	136	125
Intangibles, accumulated amortization	828	792
Common stock, par value	$ 0.01	$ 0.01
Common shares, authorized	1,000,000,000	1,000,000,000
Common shares, outstanding	333,851,337	332,472,779
United Airlines, Inc.
Receivables, allowance for doubtful accounts	20	13
Aircraft fuel, spare parts and supplies, obsolescence allowance	136	125
Intangibles, accumulated amortization	$ 828	$ 792
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