Derivatives (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Fuel Contracts [Member]	Mar. 31, 2012 Fuel Contracts [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net			$ 77	$ 196
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	113
Derivative, Collateral, Obligation to Return Cash	$ (69)	$ (62)