Fair Value Measurements (Activity For Level Three Financial Assets And Financial Liabilities) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Auction Rate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at January 1	$ 119	[1]
Acquired in Merger			117	[1]
Settlements	(10)	[1]
Gains reported in earnings	3	[1]
Reported in other comprehensive income (loss)	1	[1]	2	[1]
Balance at December 31	113	[1]	119	[1]
EETC [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at January 1	66	[1]	51	[1]
Settlements	(4)	[1]	(4)	[1]
Reported in other comprehensive income (loss)	(2)	[1]	19	[1]
Balance at December 31	$ 60	[1]	$ 66	[1]

[1] For 2010 and 2011, United's only Level Three recurring measurements are the above enhanced equipment trust certificate ("EETC") securities.