Financial Instruments and Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) (USD $) In Millions	Jun. 30, 2011		Dec. 31, 2010
Restricted Cash [Member]
Restricted cash	$ 160	[1]	$ 160	[1]
Restricted Cash [Member] | Level 1 [Member]
Restricted cash	160	[1]	160	[1]
Restricted Cash [Member] | Level 2 [Member]
Restricted cash		[1]		[1]
Restricted Cash [Member] | Level 3 [Member]
Restricted cash		[1]		[1]
Foreign Currency Derivatives [Member]
Foreign currency derivatives	(3)		(7)
Foreign Currency Derivatives [Member] | Level 2 [Member]
Foreign currency derivatives	(3)		(7)
Cash and Cash Equivalents [Member]
Cash and cash equivalents	7,519		8,069
Cash and Cash Equivalents [Member] | Level 1 [Member]
Cash and cash equivalents	7,519		8,069
Fuel Derivatives, Net [Member]
Fuel derivatives, net	191		375
Fuel Derivatives, Net [Member] | Level 2 [Member]
Fuel derivatives, net	191		375
EETC [Member]
EETC	65		66
EETC [Member] | Level 3 [Member]
EETC	65		66
CDARS [Member]
Short-term investments	196		45
CDARS [Member] | Level 1 [Member]
Short-term investments	196		45
Other Fixed Income Securities [Member]
Short-term investments	75		15
Other Fixed Income Securities [Member] | Level 1 [Member]
Short-term investments	75		15
U.S. Government and Agency Notes [Member]
Short-term investments	47		39
U.S. Government and Agency Notes [Member] | Level 1 [Member]
Short-term investments	47		39
Corporate Debt [Member]
Short-term investments	397		135
Corporate Debt [Member] | Level 1 [Member]
Short-term investments	397		135
Auction Rate Securities [Member]
Short-term investments	121		119
Auction Rate Securities [Member] | Level 3 [Member]
Short-term investments	121		119
Asset-backed Securities [Member]
Short-term investments	224		258
Asset-backed Securities [Member] | Level 1 [Member]
Short-term investments	$ 224		$ 258

[1] United's restricted cash is recorded at cost.