American Express Relationship (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Unsecured Debt	$ 794		$ 1,307
Deferred Revenue, Additions	675		675
Deferred Revenue, Future Additions in Next Twelve Months	675
Deferred Revenue, Future Additions in Year Two	675
American Express Advance Purchase of SkyMiles [Member]
Debt Instrument, Face Amount	1,000
Unsecured Debt	619	[1]	952	[1]
Fuel Card Obligation [Member]
Line of Credit Facility, Maximum Borrowing Capacity	612
Short-term Debt [Member] | American Express Advance Purchase of SkyMiles [Member]
Unsecured Debt	$ 333

[1] (5) For additional information about our debt associated with American Express, see Note 7.