American Express Relationship (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Debt Instrument, Face Amount	$ 2,243
Unsecured Debt	1,307	1,383
Deferred Revenue, Additions	675
Deferred Revenue, Future Additions in Next Twelve Months	675
Deferred Revenue, Future Additions in Year Two	675
Deferred Revenue, Future Additions in Year Three	675
American Express Advance Purchase of SkyMiles [Member]
Debt Instrument, Face Amount	1,000
Unsecured Debt	952	1,000
Fuel Card Obligation [Member]
Line of Credit Facility, Maximum Borrowing Capacity	612
Line of Credit Facility, Amount Outstanding	318
Short-term Debt [Member] | American Express Advance Purchase of SkyMiles [Member]
Unsecured Debt	$ 333