Derivatives (Narrative) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Fuel Contracts [Member]	Sep. 30, 2012 Fuel Contracts [Member]	Sep. 30, 2013 Fuel Contracts [Member]	Sep. 30, 2012 Fuel Contracts [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net			$ 337	$ 414	$ 336	$ (106)
Cash Flow Hedge Gain to be Reclassified within Twelve Months	118
Derivative, Collateral, Obligation to Return Cash	$ (75)	$ (62)