American Express Relationship (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Frequent flyer deferred revenue	$ 1,861,000,000	$ 1,806,000,000
Deferred Revenue, Additions	675,000,000	675,000,000	675,000,000
Fuel card obligation	602,000,000	455,000,000
Deferred Revenue, Future Additions in Next Twelve Months	675,000,000
American Express Advance Purchase of SkyMiles [Member]
Debt Instrument, Face Amount	1,000,000,000
Frequent flyer deferred revenue	285,000,000
Fuel Card Obligation [Member]
Line of Credit Facility, Maximum Borrowing Capacity	$ 612,000,000